How do you edit genesis roms?

To edit Genesis ROMs, you'll need a few tools: a hex editor to modify the binary data directly, and a specific ROM hacking tool designed for Genesis games, like Gens or Tiled for graphics. First, back up your original ROM. Then, use the hex editor to change values, or the ROM hacking tool to edit graphics, levels, or text. Always test your changes in an emulator to ensure they function as intended.