itch.io

I don't think you'll be able to edit roms in GB Studio, because the roms weren't compiled in GB Studio. If you are looking to make rom hacks, I do suggest you look elsewhere. I think GB Studio is primarily designed for creating your own stuff, not editing stuff that already exists.

You won't be able to do that. The best option you have is something like this: https://github.com/pret/pokered