If Ouch renamed choices too, then the changes are stored in the persistent file as well which can break saves from a patched version in non-IC version.
Well, I did not rename choices, but I did up an option for the dialogue with Dr Silver where Myriam talks about her fantasies, it made no sense to put the incest back in, and then do not include the incest in her fantasies - though that is only for chapter 3.
There is one variable added, that is due to a request to make the incest patch compatible with the mod by Bibifoc that allows to change the name of the characters.
But also, it seems that Renpy does not really save only the variables values, but also some kind of marker/bookmark that makes reference to the precompiled rpyc file (which makes sense, since it needs to save also at what point of the story you are).
The rpyc are the compiled form of the rpy that contains the dialogue - I guess till when the difference is just in the value of some byte, it's kind of OK, but the moment you have a difference in length of the text, the save may reference to a location, where it does not find what it expects, and you get the crash.
It has some resilience, some time loading a patched save using the unpatched version (to prepare the updates), it will bring me instead of at the exact point, a bit before, and then go forward with the new content, but trying to go backwards while after loading a patched save in an unpatched game, is pretty sure to give an error.
At least, that is my experience and understanding, though I am not an expert of Ren'py.