*Grmbl* ... you could always do what I did when I wanted snow for my 1.8.1 file. Cropped out the whole thing with MCEdit as far as my creation reached at the time and planted them smack in the middle of a a forest (or whatever you call it) biome next to a tundra. Just keep creating new worlds until you get a suitable one.
i too am interested in something like this. the way i understand it is when a new update converts a world, the seed changes which screws up all the biomes in your world. now if there were a tool to find out what the seed of your world is before the update and another tool to somehow change the seed back i think it would work. but unfortunately i was not able to turn up much of anything to do that. the closest i came were some outdated mods that let you do world editing. one was a plugin for a bukkit server that was updated for 1.0 i beleve. ive also been trying to find a way to disable winter biomes alltogether because they **** me off. i can deal with other biomes getting switched arround but the snow and ice just become eyesores.
The Meaning of Life, the Universe, and Everything.
I myself somewhat need a way to change biomes in chunks. I am making an adventure map where I am creating all the land myself (Being it is flying islands). And being I have used the flatgrass world for this (To delete lots of land very fast and to get rid of the void fog) it is a big pain that there are no biomes for some of the areas of this map like the snow island or the desert island.
It doesn't appear anyone has found a solution to the problem yet.
I myself make custom maps which range up to a few hundred kilometers in size. The the thing that really annoys me are the little tundra biomes that are about 100 meters in diameter. It's very frustrating to have to keep deleting random areas of snow.
A mod that lets you configure biome settings would be great, but as far as I know, no such thing exists.