We're sorry, but we have tried this before, and unfortunately this is not possible due to how the game flow is coded and it will create many in game errors and complications. Enabling save in the case file will also cause the same error. However an autosave file should be available once you reached an ending. And once you have finished an ending, and it jumps back to the character select page, a new option will be available in each characters case file to see endings you have and try to get new ones. Previously crossed out chapters should also be unlocked or replay-able in this mode.