Summary:

• Birthsigns are more uniform; each has a passive effect and a power
• The powers reflect more zodiac-style character traits rather than supernatural feats
• No more once-a-day bullshit, all powers are "lesser" but have downsides to balance them
• All vanilla assets preserved; no birthsigns added or taken away
• Two versions; one that works with vanilla and an enhanced version that requires Av Latta Magicka
  

Overview
The vanilla Birthsigns are a mixed bag. A couple of them are so powerful that they're amazing in any build, and others are made obsolete relatively early on. Some of them gave some very useful attribute bonuses, others gave you powers you could only make use of once a day. And, while I respect it was a design choice, many of these powers seemed to be outlandishly "superhuman" for what is essentially a horoscope. I've gone over and redesigned each one with this vision in mind, and hopefully each is viable enough without being too universally powerful.

1. All birthsigns (for the most part) now have a simple passive ability and a lesser power. I didn't like the disparity between some perks being completely passive and others only giving powers in some form. For the most part, the permanent increases to attributes and spell absorption (looking at you, Atronach) outweighed even some of the better power-based birthsigns. For those, they would need to be pretty damn good powers to be worth taking, which for the most part they weren't. Some powers even get replaced relatively early in the game and become useless at higher levels. I've rectified this by giving a slight passive benefit to all birthsigns (except Serpent) alongside a zero-cost lesser power that has a downside, all designed to have situational use and be lore-friendly.
2. Your birthday doesn't mean you can turn invisible. This was more a design choice on my part, but I disliked that picking what is essentially the Elder Scrolls version of a zodiac sign could give you crazy powers. I know this is a world with magic and many gods and demons and all that stuff, I just wanted to tone this down a bit, and provide reusable powers that represent great feats that reflect the character and personality of each sign. Some signs, particularly magic birthsigns, are still intrinsically magical in nature, as this is a fantasy world after all.
3. Goodbye Greater Powers, once-a-day uses are a thing of the past.  Another personal design choice, but mechanically I don't like powers that can only be used once a day. You could easily lose track of when you last used it (and when it'd be ready again), you could avoid using it out of fear of needing it deeper into a dungeon or quest, and if you missed a touch or target based greater power, it could be punishing. I think Greater Powers still have their place, but for birthsigns you choose at the start of the game, I decided to give them lesser powers instead; repeatable as often as you like, with a downside so that you can't just spam them all the time. Many of these downsides are minor Damage Attribute effects, which also provides a use for alchemy ingredients and potions that restore those attributes.
4. All birthsigns have been given attention, and none have been added. I think it's important to fix up and improve existing content, more-so than adding extra content that just makes everything before it forgettable. A minor point, but it was my deliberate intention to try and give all of the birthsigns utility and a reason to choose them, and to make the best birthsigns less overpowered while still preserving their essence. All of my design choices were made through researching pre-existing lore on the birthsigns and cosmology in general on UESP.net
5. Completely standalone, but an improved version exists with an extra dependency. Some of the decision to start the COCC project was spurred by the existence of Av Latta Magicka, and the new magic effects it adds to the game. I saw an opportunity to integrate some of these into the racial traits and birthsigns. HOWEVER, I knew not everyone was going to use that mod, so I made a version that works perfectly well with vanilla Oblivion, which is only slightly inferior (though I really do recommend Av Latta Magicka, its the only magic overhaul thats up to date, balanced, and not riddled with bugs)

List Of Changes

Spoiler:  

Show

Birthsigns

Apprentice
"Those born under the Apprentice are curious and impetuous (+10 Willpower). Always chasing progress and choosing shortcuts over hard work, they are capable of great magical feats (Temporarily regenerate magicka rapidly, at the cost of damaged Intelligence)."
(Passive) Apprentice's Curiosity: +10 Willpower
Vanilla: +10 Willpower, +50 Magicka
(Power) Apprentice's Tenacity: Restore Magicka 10pts for 30s, Damage Intelligence 5pts

Apprentice was a poor choice in vanilla, as being 100% weak to magic is not an effective tradeoff for 100pts of magicka. I instead took inspiration from the lore and Skyrim's Apprentice stone and gave it the ability to regenerate magicka faster; with a passive willpower boost and also via its lesser power. Overusing the power will lower your magicka pool significantly, especially in Av Latta Magicka where Intelligence is more important. All Mage birthsigns in the vanilla version have +50 magicka in addition to their passive, as total magicka is heavily dependent on birthsigns and racials (Av Latta Magicka makes class choice and Intelligence more important).

Atronach
"Those born under the Atronach have a strong, although burdened, spirit (Fortify Magicka 100pts, Stunted Magicka). Adapting to strife, they have the uncanny ability to absorb magicka from incoming spells, though they often lose touch with their humanity (Temporarily resist and absorb half the magicka of incoming spells, at the cost of damaged Personality)."
(Passive) Atronach's Burden: +100 Magicka, Stunted Magicka
Vanilla: +150 Magicka, Stunted Magicka
(Power) Atronach's Thirst: Spell Absorption 50pts for 30s, Damage Personality 5pts

Not much has been changed here, except a slight nerf to the Atronach. In Vanilla, this sign's spell absorption was so crazy powerful, that it was a top pick even for characters that didn't use any magic. I've locked that behind its lesser power now, with the caveat that Personality is damaged every time you use it. Probably the most inconsequential attribute to be lowered, but it'll still be a pain in the arse if you don't restore it and let it get too low. Av Latta Magicka also optionally nerfs Spell Absorption, but not enough that it makes this power worthless IMO. All Mage birthsigns in the vanilla version have +50 magicka in addition to their passive, as total magicka is heavily dependent on birthsigns and racials (Av Latta Magicka makes class choice and Intelligence more important).

Lady
"Those born under the Lady are tolerant and patient (+10 Endurance). Their unwavering focus and resolve helps them overcome hexes and maledictions cast on them by the wicked (Moderately powerful dispel on self, but damages fatigue)."
(Passive) Lady's Patience: +10 Endurance
(Power) Lady's Resolve: Dispel 100pts, Damage Fatigue 50pts

Lady still retains most of its appeal from vanilla (Endurance is just really nice to have), in addition to having the ability to shrug off negative spell effects of moderate power (or chip down stronger ones in Av Latta Magicka). Not a good idea to spam this ability in combat, or you'll faint, but a convenient power to have on hand.

Lord
"Those born under the Lord are healthy and proud (Regen 1 Health per Second). Under duress, they are incredibly resilient, stiffening themselves as they brace in the face of peril (Temporarily increase resistance to physical damage, at the cost of damaged Agility)."
(Passive) Lord's Vigour: Restore Health 1pt per second
(Power) Lord's Resilience: Shield 35pts for 30s, Damage Agility 5pts

Lord was an ok choice in vanilla, with a cheap restore health spell but a minor weakness. I instead made Lord have a small passive health regen, which especially helps in early game, and is a little more in line with this mod's design choices than a magic healing spell. To accentuate Lord's role as a defensive pick, I made it's power a potent Shield effect. Damaged Agility isn't too serious of a downside, but it'll lower your fatigue and make you more likely to be staggered as it gets lower and lower.

Lover
"Those born under the Lover are passionate and alluring (+10 Personality). Their honeyed words can easily captivate their audience, though others are often left feeling cheated or manipulated when they come to their senses (Powerful charm spell, but lowers the target’s disposition)"
(Passive) Lover's Allure: +10 Personality
(Power) Lover's Seduction: Charm 50pts on Touch for 30s, Lower Disposition by 10pts at end of duration

A paralyzing touch power was a weird pick for this birthsign compared to the lore behind it. I instead made it more like a birthsign that a diplomatic character would make good use of. The lesser power will make trading and speechcraft a complete cakewalk, until you use it enough times and end up with several people who hate your guts... I'd recommend increasing your disposition with these NPCs after a couple uses, especially since some of them will become hostile at low enough disposition.

Mage
"Those born under the Mage are bright and insightful (+10 Intelligence). They are talented spellcasters, and well aware of it, often to the point of arrogance or apathy (Temporarily increase spell power, at the cost of damaged Willpower)."
(Passive) Mage's Acumen: +10 Intelligence
Vanilla: +10 Intelligence, +50 Magicka
(Power) Mage's Aptitude: +20% Spell Power for 30s, Damage Willpower 5pts
Vanilla: +25 to all spellcasting skills for 30s, Damage Willpower 5pts

Mage was such a boring sign in vanilla, with its small magicka bonus and nothing else to offer. I've instead given it a power that reflects it's lore; people born under this sign are naturally more talented at spellcasting. The enhanced version makes all your spells more powerful, while the vanilla version reduces their costs and allows you to cast spells 1 level of mastery above your own (being able to cast Journeyman spells while only being an Apprentice in the relevant skill, for example). All Mage birthsigns in the vanilla version have +50 magicka in addition to their passive, as total magicka is heavily dependent on birthsigns and racials (Av Latta Magicka makes class choice and Intelligence more important).

Ritual
"Those born under the ritual are blessed by the immutable power of the celestial bodies above Nirn (Immune to Silence). Their connection to the higher powers helps protect them against harm and ailment (Cure poison and disease on self, at the cost of damaged Health)."
(Passive) Ritual's Word: Immune to Silence
Vanilla: +10 Resist Magicka, +50 Magicka
(Power) Ritual's Prayer: Cure Poison, Cure Disease, Damage Health 5pts for 5s

Ritual's representation has been a little inconsistent across games, but I wanted to lean into it's lore and focus on its generally useful healing potential and less on the more niche benefits associated with it (Turn Undead, Conjuration etc.). Av Latta Magicka adds the Resist Silence magic effect, and this birthsign's passive gives it 100pts of that effect, meaning characters with this sign can never be silenced. The vanilla version instead gives a little bit of magic resistance, as silence resistance isn't available. That, along with it's ability to cure poison and disease at will, makes it a decent utility/defensive focused pick for mages. All Mage birthsigns in the vanilla version have +50 magicka in addition to their passive, as total magicka is heavily dependent on birthsigns and racials (Av Latta Magicka makes class choice and Intelligence more important).

Serpent
"Those born under the Serpent share no particular traits, besides being the most blessed, and most cursed, of individuals. Their presence means danger, and they have a knack for bringing misfortune and hardship wherever they go (Temporarily increases a target’s vulnerability to damage, but also increases your own)."
(Passive) None
(Power) Serpent's Curse: Expose & Weakness to Magic 50pts on Target for 30s, Expose & Weakness to Magic 20pts on Self for 30s
Vanilla: Weakness to Normal Weapons & Magic 50pts on Target for 30s, Weakness to Normal Weapons & Magic 20pts on Self for 30s

The only birthsign I didn't give a passive, as a nod to the lore. Instead, it has a particularly useful lesser power that will make you excel at 1 on 1 combat. Using this power is not advised if you are outlevelled or outnumbered however, as its drawback means enemies will quickly rack up damage on you.

Shadow
"Those born under the Shadow are deft and composed (+10 Agility). Calculating and often cold, they prefer to take the slow road and avoid danger rather than confront it directly (Temporarily move faster and avoid detection, at the cost of damaged Speed)."
(Passive) Shadow's Sleight: +10 Agility
(Power) Shadow's Prowl: Chameleon 20pts, Fortify Sneak 25pts & Fortify Speed 15pts for 30s, Damage Speed 5pts

A birthsign I hated in every way in vanilla, and it was one of the weakest considering how quickly it could be replaced. Giving it an attribute boost as a passive and a lesser power that increases your ability to avoid detection temporarily helps make it more desirable for sneaky characters. Overuse increases the Shadow's natural hesitancy and caution, and lower your speed. HIGHLY RECOMMENDED that you set bUseRefractijavascript-event-stripped1 to 0 in the Oblivion ini or use a mod that does something similiar; this makes you only partially transparent relative to the level of Chameleon effect on you (instead of completely invisible regardless of how strong your Chameleon is). This is not only an improvement overall (in my opinion), but it fits the intention of this power better.

Steed
"Those born under the Steed are swift and headstrong (+10 Speed). Lively and energetic, they often push themselves harder than they should when need arises (Temporarily increase athleticism and carrying capacity, at the cost of damaged Strength).
(Passive) Steed's Fervour: +10 Speed
(Power) Steed's Venture: Feather 100pts & Fortify Athletics 25pts for 180s, Damage Strength 5pts

Steed trades some of its vanilla passive power for a useful lesser power which'll help you get home with more loot and potentially escape dire situations. Overusing this power will cause great strain on your character, and your Strength will suffer.

Thief
"Those born under the Thief are risk-takers by nature (+10 Luck). They excel at getting themselves out of the messy situations they often face, but by tempting fate, their luck will eventually run out (Temporarily avoid damage to escape harm, at the cost of damaged Luck)."
(Passive) Thief's Fortune: +10 Luck
(Power) Thief's Gambit: Ethereal Form 5s, Damage Luck 5pts
Vanilla: Resist Magic & Normal Weapons 100% for 3s, Damage Luck 5pts

Everything about the Thief has been tailored towards its lore and its iteration in Morrowind. Still the best way to get extra Luck in game and passively increase all your skills, and the lesser power will allow you to escape dangerous situations, although you won't be able to attack during this time. In Vanilla, there is no Ethereal Form effect, so to compensate for the fact you'll be invulnerable to almost all damage and still be able to attack, the effect is a couple seconds shorter. Damage Luck is deceptively inconvenient and you'll want to keep on top of that.

Tower
"Those born under the Tower are perceptive and cautious (+10% Shield). They often stop to observe or contemplate before they engage, being gifted with remarkable sense and awareness (Briefly immobilize yourself to detect targets around you)."
(Passive) Tower's Caution: +10 Shield
(Power) Tower's Gaze: Detect Life & Death 200pts for 5s, Burden 1000pts for 5s
Vanilla: Detect Life 200pts for 5s, Burden 1000pts for 5s

Instead of 2 pretty mid greater powers, you'll now get a passive ability and a lesser power that reflect the cautious & perceptive nature of the Tower, as influenced by the lore and Morrowind's iteration of the sign. The power should help you get a quick idea of what you're up against before you engage in a fight or situation. Vanilla doesn't have Detect Dead, so there's a slight nerf in that version of the mod, but otherwise the utility is the same.

Warrior
"Those born under the Warrior are strong and direct (+10 Strength). Quick to anger, their ferocity is unmatched, though they often exhaust themselves with their own temper (Temporarily increase physical damage output, at the cost of damaged Endurance)."
(Passive) Warrior's Might: +10 Strength
(Power) Warrior's Rage: Fortify Attack Damage 7pts for 30s, Damage Endurance 5pts
Vanilla: Fortify Strength 50pts for 30s, Damage Endurance 5pts

While you don't get an Endurance boost from this birthsign anymore, at least you get a particularly powerful boost to attack damage available via it's lesser power. To balance this, Damage Endurance is one of the most severe stat drops you can receive, as it'll lower your max health (especially in Ascension, which I highly recommend). For the vanilla I was unfortunately stuck with Fortify Strength as an effect, which unless you use a mod which uncaps attribute boosts past 100, will become less useful as your raise your Strength attribute, but it was the best analogue I had unfortunately.



Compatibility
Obviously incompatible with other Birthsign mods, but will work 100% with anything that doesn't touch the birthsigns (and fits in perfectly with Through the Valleys and as an alternative to mods within Dispensation's Comprehensive Modding Guide). If there are any niche incompatibilities or issues with bash tags, let me know or feel free to send me a patch.
This mod is the second of three planned mods that will make up COCC (Completely Overhauled Character Creation). The first mod covers classes, and the third will cover races. The third and final instalment shouldn't be too much longer, as well as a merged version of all three mods.