In the JSON docs the biome field says Biomes can be specified by their registry-name or by using a BiomeDictionary ID.
I know registry names for biomes (e.g. minecraft:forest, minecraft:mesa, etc) but I need to get every mesa biome subtype (plateau, M, etc) to not write every id for the mesa biomes or every id for every extreme hills biome

Nevermind, found it: https://github.com/MinecraftForge/MinecraftForge/blob/1.11.x/src/main/java/net/minecraftforge/common/BiomeDictionary.java#L44-L90