Before your competition: YES
Edit your Criteria as much as you need to! Check out our best practices here.
During your competition: NO
You cannot edit criteria while a competition is live. If you absolutely must edit the criteria, close the competition by shifting the start time. Change the start time back to re-open the event.
After your competition: YES*
Edit your criteria as needed. Of course, we don't recommend changing your Criteria after the competition ends, because that wouldn't be terribly useful as a record of what happened at your competition.