CREDITS
Skins were reformatted, tested, and put together by TerraTerraCotta
(These Skins were tested using MoreAnimals and Adopt N' Skin)
Beta Pichu Sprites were originally created by Mister Mike of the Spriter's Resource
Source: https://www.spriters-resource.com/custom_edited/pokemoncustoms/sheet/109033/
Canon Sprites are ripped from HeartGold and SoulSilver (also used from the Spriter's Resource)
DISCLAIMER
THIS IS NOT A MOD/CONTENT PATCHER FILE ON IT'S OWN. These are merely formatted skins that can be used with other mods.
HOW TO USE
(In all cases it's helpful to refer to the READMEs of the re-skin mods you are using. However I'll offer a lite summery here.)
NOTE: BabyRabbit and Rabbit are the Male version, BabyRabbit_2 and Rabbit_2 are the Female version.

MoreAnimals
In your Mods folder go to MoreAnimals>Assets>Skins

Pick a Pichu file and label it as "BabyRabbit" (If you already have other Baby Rabbit skins, label it with an "_Number". For example "BabyRabbit_5")

Pick a Pikachu file and label it as "Rabbit" (Same rule as the BabyRabbit, However you should make sure that the number corresponds what you chose for the Baby Rabbit!! So if you named the Pichu file "BabyRabbit_5" then your Pikachu should be "Rabbit_5")
You now have a chance of getting a Pichu when you adopt a new bunny!
DIYCP - Animals
In your Mods folder go to [CP] DIY-Animals>Assets
Replace the "BabyRabbit" and "Rabbit" files with the Pichu skin of your choice.
This should turn all the rabbits into Pichu/Pikachu depending on what you chose.
Adopt 'n' Skin (Animal Skinner)
In your Mods folder go to AdoptSkin>Assets>Skins

Pick a Pichu and label it as "BabyRabbit" (If you already have other Baby Rabbit skins, label it with an "_Number". For example "BabyRabbit_5")

Pick a Pikachu file and label it as "Rabbit" (Same rule as the BabyRabbit, However you should make sure that the number corresponds what you chose for the Baby Rabbit!! So if you named the Pichu file "BabyRabbit_5" then your Pikachu should be "Rabbit_5")
Almost completely the same as MoreAnimals