Lore-Friendly Expanded Birthsigns takes strong inspiration and direction from "Expanded Birthsigns For Purists". Indeed, this mod was created because no file for that mod could be found. Although the mods are similiar, "Lore-Friendly Expanded Birthsigns" takes things in some different directions. The mod adds 13 new birthsigns(14 planned), many based on previous games in the series, and rebalances all existing birthsigns. It also revises their flavour to bring the astrological aspect more into prominence, in ways that are hopefully consistent with the established lore.

Install:

Copy the .esp to your data folder and add it to your load order.

Oblivion Mod Manager: It adds spells, so you should probably used a Bashed Patch. See Wrye Bash.

Wrye Bash: Add it, then Bashed Patch. There's a wizard, but you don't really need it. It's just there for future updates and expansions.

If you install the Vanilla Magic version, then Fortify Magicka Multiplier bonuses are:
The Mage: 120%
Elfborn: 170%
Mageborn: 150%
Wombburn: 200%

Updating:

You should probably make a backup first. I have no idea.

Incompatabilities:

Other mods that change birthsigns or rely on the exact vanilla birthsigns, I guess?

Uninstalling:

Probably not a good idea. Make a backup first?

Version:

Beta 0.10.0

Birthsigns:

Thief:
---Masser- Rogue
*Ability* The Thief: +10 to Agility, Speed, and Luck.
---Secunda- Danger Sense
*Ability* Danger-sense: +15 Agility, +5 Speed, and Detect Life 10 ft.

Warrior:
---Masser- Warwyrd
*Ability* Warwyrd: +15 Strength, Resist Normal Weapons 10%.
---Secunda- Warborn
*Ability* Warborn: +10 to Strength, Agility, and Endurance.

Mage:
---Masser- The Mage
*Ability* The Mage: Fortify Magicka Multiplier (150%)
---Secunda- Fey
*Ability* Fey: +10 to Intelligence, and Willpower.
*Power* Manawell: Restore Magicka 10 for 5 seconds (50) (once a day).

Apprentice:
---Masser- Elfborn
*Ability* Elfborn: Fortify Magicka Multiplier (250%), Weakness to Magicka 50%, Weakness to Fire, Frost, Shock, 15%.
---Secunda- Mageborn
*Ability* Mageborn: Fortify Magicka Multiplier (200%), Weakness to Magicka 50%.

Lady:
---Masser- Lady's Favour
*Ability* Lady's Grace: +10 to Personality, Agility, and Endurance.
---Secunda- Lady's Heart
*Ability* Lady's Heart: +10 to Intelligence, Willpower, and Endurance.

Lord:
---Masser- Trollkin
*Ability* Trollkin: 25% Weakness to Fire, Restore Health 1 (Constant Effect).
---Secunda- Lordly Graces
*Ability* The Lordly Graces: +10 to Strength, Willpower, and Personality.

Tower:
---Masser- The Warden
*Ability* Unmovable Will: +10 to Willpower.
*Power* Tower Key: Open on touch, Hard (once a day).
*Power* Tower Warden: Resist Normal Weapons and Reflect, 25 points each for 120 seconds (once a day).
---Secunda- // Not yet worked out.

Shadow:
---Masser- Nightfriend
*Ability* Shadowbender: +10 to Personality, +10 to Illusion.
*Power* Shadowmeld: 70 pts Chameleon on self for 30 seconds (once a day).
---Secunda- Moonshadow
*Ability* Silent Step: +10 to Agility, +10 to Sneak.
*Power* Moonshadow: Invisibility on Self, 60 seconds (once a day).

Ritual:
---Masser- Called
*Ability* Divine Might: +10 to Strength.
*Power* Mara's Gift: Restore Health on self, 200 for 1 second (once a day).
*Spell* Blessed Word: Turn Undead on target, 100 for 30 seconds.
---Secunda- Firewalker
*Ability* Firewalker: +10 to Willpower, +15 to Personality, 25% Resistance to Fire.

Lover:
---Masser- Captivating
*Ability* Dancer's Grace: +10 to Agility.
*Ability* Mooncalf's Gaze: +15 to Personality.
*Ability* HeartSpeech: +5 to Speechcraft.
---Secunda- Dancer
*Ability* Dancer's Grace: +10 to Agility.
*Power* Lover's Kiss: Paralyze target 10 seconds, Damage Fatigue 120 for 1 second on self (once a day).

Steed:
---Masser- Charioteer
*Ability* Charioteer: +20 to Speed, +10 to Agility.
---Secunda- Cavalry
*Ability* Cavalry: +10 to Speed, Endurance, and Agility.

Atronach:
---Masser- Wombburn
*Ability* Wombburn: Stunted Magicka, 50% spell absorption, Fortify Magicka Multiplier (300%)
---Secunda- Golem
*Ability* Golem: Stunted Magicka, 35% spell reflection, 15% Resist Normal Weapons

Serpent:
---Thief alignment- Star Cursed
*Ability* Luck of the Low: +20 to Luck
*Power* Star-Curse: Poison 3 pts on touch for 30 seconds, Damage health on Self, 1 pt. per second for 30 seconds (once a day).
---Mage alignment- Cold Blooded
*Ability* Cold Blood: Resist Magicka (50%), Resist Fire 25%, Weakness to Frost 50%.
*Power* Soulmolt: 50 points Reflect Spell and Shield on self for 30 seconds, cure poison, paralysis and disease, and dispel 100% on self (once a day), for 35 points of damage.
---Warrior alignment- Serpentine
*Ability* Serpentine Aspect: +10 to Strength, and Agility.
*Power* Constrictor: Drain each 20 points for 30 seconds Agility and Speed, and inflict a 100-point Burden on touch for 30 seconds (once a day).