I tracked down the code that fills chunks with stone, and it looks like the stone is generated first then the biome blocks are placed. Not sure what to do with that. Do you happen to know the event that I can use instead?
Also, I managed to stop mobs from spawning here.( When I disabled creature spawning, I forgot to disable monster spawning.) I want the biome to only spawn wither skeletons. I made the biome spawn normal skeletons, how can I get wither skeletons to spawn?
Please Note: I am not trying to replace the stone in all biomes. I only want my custom stone to generate in my custom biome. All other biomes won't be changed.