This^It is possible. I've played a number of XP games that have done this, and I'm fairly sure that it's possible in Ace.
But what those who have done it are unanimous about is that it has to be planned that way from before you start the first game. It's not possible to introduce it later on. You also have to be prepared for an enormous amount of extra work.
You can still edit the numbers, but don't switch around anything otherwise you'll have some major issues going on. Also No adding scripts after the first chapter. Your saves won't carry over well.This^
The file documents are kept in the base folder for your game, transferring that file alone to another game folder is no problem. The save file keeps track of just about everything the player has done in the game so far (switches turned on/off, variables, items and equipment, etc.) However, you need to make sure all the items, weapons, armors, actors, and many other objects in the database are either left the same or completely untouched.