The checksum is currently not fully understood. Currently, I can patch the checksum for small edits like held money, but bigger edits need a full recalculation. In addition, the save size varies. In order to find something in the save file, one must first read the previous data. A while ago I did research on held items, so in the future, those may be editable, but then we come back to the checksum problem.
It seems GTI and Super MD use the same game engine (and they probably have similar save structures), so maybe more people will be motivated to help research in the future.
[Edit] Oh, and I suspect Datel used RAM hacks to change the Pokemon. After all, the checksum is tricky, and they have no codes, only edited saves.