Uh... you can still update your entry as much as you like up to the deadline, Sherman.
For this challenge im going to say no. You have 2 weeks to work on your entry. If you arnt quite happy enough with it, dont submit it as early. In a duel you only get one chance to beat your opponent, you cant have multiple attempts, or retry a move. So similar to that, what you submit is what will be placed against the opposing person. You have one chance / opportunity to beat them, so you should make sure you are pleased with it when you submit. 2weeks should be long enough to ensure this.