I would just backup the whole profile regardless. Just go to drive C: then look for your windows user name then \Documents\Rockstar Games\GTA V\Profiles\ and copy that folder to the desktop or something then start a new game. If it doesn't mess with your online saves, then your good. If it does, you are still good, just copy that file back to the same original location. In fact, you might want to copy the whole GTA V main folder. In that last folder "profiles" there should be two sub-folders. I'm guessing one is the SP campaign profile and the other the MP online profile. On mine, though, they are random letters and numbers so I can't tell which is which.