CollosalPokemon and I have been researching the savegame structure of the Devil's Survivor DS game. From the research findings, I've coded a web-based savegame editor in PHP. Currently only raw savegame files are supported by the web-based version, but other formats will be allowed soon. The web-based savegame editor can be found at:
Research on the game's checksum algorithm is incomplete. If you make too many changes to your save file, then the game will report the save as "corrupt." Always remember to backup your save file before editing it! If you find any bugs, please report them in this thread.
If you would like to contribute to our efforts, see the GitHub repository below: