SUPPORTED VERSION(S): Alternate/Alternate-Beta (Right click game > Properties > Betas > Alternate)
Normal branch isn't supported since it uses IL2CPP (I might do this eventually, no promises)

For normal branch (Follow from step 2) however you can download the zip and use the included text file to add more tattoos (only tattoos) and add clothing items to other slots as normal. So basically the example provided for tattoos below would just have UpperBodyTattoos and FaceTattoos in your case (with the path) and any other tattoos - just NOT clothing items.

AGAIN. This mod ONLY makes it so tattoos can be used to wear things beyond tattoos as it's the only thing in appearance.json that goes through Tattoos as an array. This does NOT add any items to your inventory - as stuff like policecap are not valid items.

Currently without this mod you can equip the police gear just fine but not all of it, and you might want extra stuff like a watch, necklace, or maybe wear multiple hats, I don't know what you're in to. At the least you could pretend to be a cop with all the gear, put some tattoos on, wear a watch and a chain, and then slap on a respirator.
It won't stop you looking like an idiot, though. This mod can't help with that.

Setup (Alternate Versions)
1. Throw the wearmore.dll in \steamapps\common\Schedule I\Mods and you also need MelonLoader.
2. Paste this into the URL bar of file explorer %userprofile%\AppData\LocalLow\TVGS\Schedule I\Saves\ then navigate through it into your Players folder, (you're likely player 0) and then edit Apperance.json in whatever you want.
3. Make changes. The tattoo section is what this mod changes to allow more than just tattoos. Some things might not work in the tattoo slot, however. Here's an example of what mine looked like from one of the photos:
    "Tattoos": [
        "Avatar/Accessories/Waist/PoliceBelt/PoliceBelt",
        "Avatar/Accessories/Head/PoliceCap/PoliceCap",
        "Avatar/Accessories/Chest/BulletproofVest/BulletproofVest_Police",
        "Avatar/Layers/Tattoos/UpperBodyTattoos",
        "Avatar/Layers/Face/FaceTattoos1"
    ]
4. Anything you place in the tattoo slot will appear white on the character. This cannot be changed. If you want to adjust the colours, use another slot like Top, Headwear, or Bottom, etc and adjust the colours there. * Note that this mod does NOT change those slots to support more than one thing at a time.
5. Remove ALL clothing in-game (Tab and at the top of the screen, Character). You will need to save and then reload your save for it to appear in-game.

NOTE: Tattoo parlor will likely not work if you add things to tattoos slot.

If you have any questions or I didn't make it clear, tell someone else (but ideally me since nobody else is going to help or fix it)
But, if you follow this disjointed mess, you'll probably have no problems... hopefully.

As a bonus, I mined some of the files and found a list of items. Here you go: (i.e give SmallRoundGlasses in console)
Cash
CargoPants
Jeans
Jorts
LongSkirt
Overalls
Skirt
LegendSunglasses
RectangleFrameGlasses
SmallRoundGlasses
SpeedDealerShades
CombatBoots
DressShoes
Flats
Sandals
Sneakers
FingerlessGloves
Gloves
BucketHat
Cap
ChefHat
CowboyHat
FlatCap
PorkpieHat
Saucepan
Apron
Blazer
CollarJacket
TacticalVest
Vest
ButtonUp
ButtonUp_Rolled
FlannelShirt
T-Shirt
VNeck
Belt
BrutDuGloop
ChateauLePeePee
GoldBar
OldManJimmys
CoffeeTable
Dumpster
FloorRack
GrandfatherClock
MetalSquareTable
TrashCan
SingleBed
SmallTrashCan
TV
WoodSquareTable
ExtraLongLifeSoil
Fertilizer
LongLifeSoil
PGR
Soil
SpeedGrow
Acid
Addy
Banana
Battery
Chili
CocaineBase
CocaLeaf
Cuke
Donut
EnergyDrink
FluMedicine
Gasoline
HorseSemen
Iodine
LiquidBabyBlue
LiquidBikerCrank
LiquidGlass
LiquidMeth
MegaBean
MotorOil
MouthWash
Paracetamol
Phosphorus
Pseudo
Pseudo_HighQuality
Pseudo_LowQuality
Viagra
FloorLamp
FullSpectrumLight
HalogenLight
LEDLight
Baggie
Brick
Jar
AirPot
CheapPlasticPot
GrowTent
MoisturePreservingPot
BabyBlue
BikerCrank
Cocaine
DefaultWeed
Glass
Granddaddy Purple
Green Crack
Meth
OG Kush
Sour Diesel
Test Weed
CocaSeed
GranddaddyPurpleSeed
GreenCrackSeed
OGKushSeed
SourDieselSeed
CheapSkateboard
Cruiser
GoldenSkateboard
LightweightSkateboard
Skateboard
BrickPress
Cauldron
ChemistryStation
DryingRack
LabOven
LaunderingStation
MixingStation
MixingStationMk2
PackagingStation
PackagingStationMk2
DisplayCabinet
FilingCabinet
Safe
LargeStorageRack
MediumStorageRack
SmallStorageRack
ElectricTrimmers
Flashlight
ManagementClipboard
TrashBag
TrashGrabber
PlantTrimmers
WateringCan
BigSprinkler
SoilPourer
Sprinkler
BaseballBat
FryingPan
M1911
M1911_Magazine
Machete
RevolverCylinder
Revolver

v0.3.4 beta items (Some cannot be given)
GoldChain
SilverChain
GoldWristWatch
SilverWristWatch
MetalSign_Built
BeachDay
Lines
Menace
Millie
Offer
Rapscallion
WallClock
WoodSign_Built
AntiqueWallLamp
ModernWallLamp
WallMountedShelf