I have not personally used anything listed here but it seems promising. https://gameboy.github.io/wiki/cartreaders https://gameboy.github.io/wiki/cartreaders

I have not personally used anything listed here but it seems promising. https://gameboy.github.io/wiki/cartreaders https://gameboy.github.io/wiki/cartreaders I believe the same or similar devices can be used to write cartridges with ROM hacks if one is so inclined.