Sorry for the late reply, I missed this comment. You probably figured this out already, but the save files are stored outside the main game files, specifically in the AppData/LocalLow/RalivDev folder. I would recommend copying and pasting the save folder elsewhere if you are worried about it being deleted/lost. If you redownload the game, it should still use the same save files, HOWEVER I have not tested this using the Itch app or any other file managing service.
For future reference, if you have followed the steps perfectly but get a checksum issue, it is likely you have a different version of the game or mod. Only the most recent version of the game available on Itch is confirmed to work with the most recent version of the mod as of now.
Finally, disabling checksum validation will never make the mod work, as a mismatched checksum inherently means it will not work.