You can have defaults with open slots. If you submit game lineups, and then make changes, it's a problem. If your left-right defaults are pretty much right but are missing, say, one position, the robot will usually pick the right player, especially if you don't give it a lot of choices.

As for pitching, it becomes more difficult to define roles. If you're away from the computer all week, I would suggest having someone you trust input the last minute changes, or better yet, find a library, log on, and do these moves yourself.

You could also ask the commish for more advice...