This mod appears to be broken.

The core functionality exists, but this isn't removable from a save game, the control to toggle it doesn't do anything, even if changed to another key. Very annoying as it conflicts with the assisted driving mod and now I'll have to start a new save.

Delete both the mods, restart game and re-save. Both are gone right? Now you can install assisted driving if you like it better.

I will try that.

It's not that I like it better, it's that the snapping plays around with the assisted driving and your hotkey, even if changed, doesn't seem to work on my game. Not sure if that's the mod itself or it's conflicting with another mod that I have, but it's not that I don't like your mod

Vehicle snapping seems to stay in my save even after both mods were removed

I can now confirm that vehicle snapping messes with the code of the game. With both mods removed and an entirely new save, the vehicles are still snapping despite no conflicting or driving/snapping related mods.

I'm sure that no mod can do that, there is something wrong with your installation. LUA scripts are incapable of modifying executables. And for that sort you need confirmation or assistance from the Factorio developers. If you want to file a bug report at:
https://forums.factorio.com/viewforum.php?f=7&sid=16b05ed1925c5061202223f7ac653133