Hi! I did only find some tools to _extract_ Biome-Infos, but is there any tool or function to change the Biome-Data for chunks?
Unfortunately, no. Minecraft does biomes a little weird - chunks store no biome information, instead it is all calculated based on the seed. This means that the biome of a given area on a given map is fixed forever.
Oh, crap. Can already see my snow biomed town that I melted become snow again agaisnt my will on next update