Not the best solution in my mind. So much work, and limited flexibility. So much more work when you get new players, different training positions, injuries, etc etc.
Having more preset line-ups, enables you to run different tactics, training. You could alter the preset when you choose it for a game. Now when you load an old game, you have to remember which game you are looking for. It is not so many games to chose from either. So what happens if you have run the same setup for a while. Even if one way to do it already exist, it has much room for improvement.