Create a custom dimension that is the same as the overworld but with a different seed.

I want to create a custom dimension that is basically the same as the overworld but as if it had been created a fresh, i.e. with a new seed. It seems like they removed the ability to assign a seed in the dimension jason file so what would be the way to go about doing this now? (very annoyed that feature got removed because it would make my life a lot easier lol).