It could go in flash... I've just never looked at how to write flash from the Genesis side. Need to do some experiments on that to see if it works right. SRAM is easy to deal with, which is why I suggested it.
ah, you want to save entered codes from the md side? then it can go to sram.
Do you know the format of those files? If so, it should be easy to handle.
.pat files are simple text files
FF5420:8000 no gravity
0251B0:4E71 debug menu
that's the contents of pat file actually. kega saves them automatically in the same directory as sram files and savestates when gg/par codes are used.
other emulators might use them too, but I never checked if that's the case.
At least in the "deluxe" version of the menu, that could be added to the Options Screen you go to when you press A over a game. Right now, the options have to do with the hardware, not the game, but in the deluxe menu, we have room to add options for cheats and other things.
well, that's the thread for the deluxe menu

you can add submenus for gg codes/hardware options.
on unrelated note, but as a request/suggestion - can you read eeprom from the md side and save it to sram and vice versa? there is no way to read/write eeprom from the pc side currently, and with focus of the neo team shifted to other flash carts, it may never be realized. also it may be implemented in such a way as to allow more than one game with eeprom to be used at the same time - copy sram to eeprom - run game, on startup check record in sram and copy eeprom to sram if needed.