Hacking SimCity 2000 saved games
log.schemescape.com
log.schemescape.com
Game Genie, Action Replay, and other similar devices worked on a different principle - the "codes" represented patches to the code in the game cartridge, not to data in memory. (The original Game Genie for the NES could patch up to three bytes.)
Hah, it's probably considered one of the greatest games of the 90s.
Contrast that with experiences like the author and the taboo joys of rooting around in the files and "hacking" something to do the thing you want.
Minecraft
When I looked on the disk, I saw that the pictures were listed as, eg LADY01 up to LADY05.
11 year old me was pretty excited when I thought, "what would happen if I renamed the files?"...