This line of thinking is entirely fabricated. Save files are legally under the player's ownership.
I got lucky knowing that is was likely that at their core, the save files were going to be JSON. The decryption algorithm was found via clean-room reverse engineering. I have not touched anything from the game folder.
Finding the IDs was a manual process of trying new IDs, repacking the save, then loading it again. I had to do this about 20-30 times to find the good few I did.