Can I edit a sealed slip?

Yes. A sealed slip has an Edit button, and it works until the match starts.

Tapping "Edit" turns your slip back into a draft: it stops counting and leaves the crowd percentages. Change whatever you like and seal it again. If the match starts while it is still a draft, it is not in play.

If you change your vote for who wins and it no longer agrees with your score, the slip reopens by itself so you can adjust the score. It has to be sealed again too.

"Start over" clears the score and every player you picked. Your vote for who wins stays.