Wow I'm lucky I asked.Yes. Start a new game with a different character, SAVE IT IN A DIFFERENT SLOT.
In order to unlock everything you need, you've got to keep one save game per character, plus a separate save game for the chapter you unlock after completing all three, then ANOTHER separate save game for the chapter you unlock after that.
Almost didn't for a moment and prob would have deleted my save.
For fucks sake Square, you shouldn't need a manual on how to save a game.
Thanks.