[1.7.10]Trouble understanding world generation

I'm having trouble understanding how how world generation works, at least enough for my purposes.

I understand what BiomeGenBase is, as well as WorldGenerator; I'm not sure how (rather, when) either of these are really used by the rest of the game.

My end goal is to create a visual separation between the 'inner' and 'outer' areas of my map, which i have separated by a wall which is created by a WorldGenerator₁. I'd like to do this by making the outer areas darker, and possibly with new biomes that spawn exclusively there. It would seem i need to understand what minecraft uses to decide which biomes to place where, so i can change this behavior. I have of course looked at the source of GenLayer, WorldChunkManager, and other BiomeGen s; but i would like to know a minimally invasive₂ way of making this changes.

₁ in some places the wall is broken by other features such as lakes, telling me that lakes are being generated after my wall. Is there a way to know or change what order WorldGenerator s are called?

₂ i would like not to affect non-biome aspects of generation from other mods, such as meteorite generation from AE2

Please and thankyou

edit: forgot version in subject