Except it will change the biome of the existing chunks.
At least, it will remove the biomes that are supposed not to exist.
That won't change the world gen, but you could end up with snow in a desert, or grass having a different color.
And near the borders, it gets crazier, because if the part already generated is a biome that doesn't exist anymore, the new chunks will have the possibility to generate their own algorithm, based on what should be there, and you can have some crazy nonsense going on.
That's pretty easy to check, just disable all biomes but one, make a new world, save and exit, disable the biome and enable an other one instead.