I can believe that that's true currently, but it would not be hard for DPC to set something up so that editing variables (via console or save edit) sets up a time bomb that he can detonate in any future release.
The simplest (and easiest to work around) would be to create a dummy variable with the sole purpose of recording the value of some flag or other long-term stable variable (like which path you choose at the end of chapter 8) and then ignore that dummy variable entirely until it's eventually checked against the actual variable, which would seem to have been changed successfully up until that check is done...
There are other tricks that can be done, depending on how much effort he wants to put in, but the basic idea remains - redundantly store multiple versions of the same information, only some copies of which are actually used for anything, and then later compare the active versions against the backups.
To check something, you need that "something" to exist, no? Save editors don't add anything new to saves, nor new variables nor something else. Dev console flag "enabled/disabled" is checked and tracked, but only to block player of getting most of Steam achievements. You can read the code and figure out where DPC added checks for enabled dev console flag and what particular achievemnts this blocks (most mini-games related ones, in short)
Regarding the rest. "Secret", "dummy", etc variables are not required at all. Because if you edit the save in the way to enable
multi-paths or any
OTHER combos that are not possible and can't work together (in short - any combos that fails checks in "if"/"ifelse"/"else" conditions in code) - you'll fuck up yourself and put a time bomb which will blown at the random moment in the future ep(s). Game will just crash with an exception or you'll get a "death-loop", as it was with most multi-paths saves in EP9 - players thought that using "harem-mod" would work well, but it didn't worked out. It wasn't even the DPCs "special" trick or something. It's just how the complexity of paths and branches works in code - DPC have to set a lot of checks for conditions and variables to serve and show players consequences of their previous choices, even in very little details. If you make a mess in variables, you're insanely increasing the chances of lookups, crashes (with code exceptions) and buggy death-loops when none conditions are met and scenes start from the beginning.
In short, edit variables wisely. Don't try to enable and/or combine things that are not possible during the normal gameplay. You can safely edit your save to fix some mistakes you made during gameplay to avoid replaying the bunch of episodes. But you have to track all those variables from the moment they set up until current moment in your game. If those variables was checked in between this particular moments - you have to check and probably correct the other ones which was set up based on the one (or several) you had edited too. Talking about
SteveyP situation - Patrick score doesn't have any checks and any new variables which is based on that score between 7-9 episodes. So it's safe to edit the score variable in the beginning of EP10.
And talking about URM 0x52 mod - you can edit any variables on the fly with it, as well as absolutely safely watch the alternate scenes, where particular conditions is not met for you current game/save. You have just to save before watching the alt scenes and then reload the save you made before. This way everything remains intact, but you can see each consequences/outcomes much faster w/o replaying the whole episode, as well as constantly see & notice every check that DPC is pulled. Yes, finding all the secret and subtle stuff is much more exciting when you do it blindly, but since game is insanely branching after EP8, this way became very complicable. This way you still can't play all of girls paths in one save, but you can see the checks for your particular MG/SG branch and see all of those alt scenes in just one run. Then you can decide how you're doing and what to fix.
Finally, since almost all RenPy games are "open source" - you can decompile/modify/recompile the whole games with almost any modifications you made to it. If you want so much - you can remove ALL of DPC's checks from scripts for cheats/mods as well. You can recompile the game using the newest RenPy engine, and so on. Or you may include altered renders and/or video files. For example - you can create your own game distributive and files set with "improved" 60fps video which is listed in the first post. Instead of putting them in as a patch and increasing the game folder size about 2 times.