Minecraft Infinity

Uhh so i'm new to this whole modding thing but I have had a mod idea since like forever, the idea of the mod is, well by its name infinite or pretty close. There's tons of things I want to add and i'm going to use MCreator until I can't. By that I mean that I want certain additions to be allowed or disabled so the mod isn't so big.

So for the first release of the mod i'm planning on giving each biome a sub biome, but to do this I also want to edit previous biomes (if anyone knows how to change vanilla biomes please tell me). The kind of sub biomes would be like Oak Forests with a sub biome of Snowy Oak Forest or Burned Oak Forests