Is it possible to turn off Vanilla biomes from generating and let generate only biomes from mod?

This is not currently possible.

There is a ticket for this to be added in the future updates on our issue tracker.

I don't think this is easily possible even if it were to be implemented into MCreator :P

Your best bet is probably to just set your biomes to some ridiculously high weights so that no vanilla biomes get much of a chance to spawn. Try something like 1000 and you'll basically never see a vanilla biome.

Actually there is a way to do this, I just need to add it into MCreator once I get a timeframe to dedicate it to this feature.

So I stumbled upon this post and wanted to ask if you guys are going to implemet it, and if yes, when?

Please at least search our issue tracker before asking such questions, it is planned.