Hello again(this may be confusing actually look at the gun texture thing) but If you mean to make a different version of a mob spawn in different biomes Im afraid you just have to make a new mob that spawns in that biome and not the other.If it is for something else you would have to kill it (after teleporting it so the player cant see) and spawn the new variant with the old mobs HP(This could potentially be very laggy).Hope I helped.Sorry if I could not.
Hello again(this may be confusing actually look at the gun texture thing) but If you mean to make a different version of a mob spawn in different biomes Im afraid you just have to make a new mob that spawns in that biome and not the other.If it is for something else you would have to kill it (after teleporting it so the player cant see) and spawn the new variant with the old mobs HP(This could potentially be very laggy).Hope I helped.Sorry if I could not.