I have created a skyblock world by setting a superflat world to generate with only air. Problem is, it doesn't seem to have any biomes other than forest. I would very much like, however, to have it generate different biomes throughout the world. Of course being skyblock there would be no natural generation of anything, but it would permit me to freeze water into ice, grow coral, etc.
Is there any way to change the biome generation settings of an existing world? Failing that, is there any way to create an empty world with variable biomes when generating from scratch (in which case I could just copy my current island to such a world)?