I took the ACT with writing in June (got a 25) and just signed up to take it again at the end of October. On the UC app, it says to self report the highest composite score from a single test date. Let’s say I submit the UC app on November 1 (totally hypothetical) with the 25 ACT score listed, but I receive the October ACT score at the end of November which ends up being higher than the 25 (again, hypothetical). Can I go back to the application and change the ACT score?
The UC application submission opens on November 1 but closes on November 30th. You have time to submit it
UCs require, in addition to the application, that you submit official test scores from the testing agencies. Those official scores, not what is shown on the application, are the ones actually used to determine admission, and those can be submitted as late as December (the UCs actually accept through the December tests even though the application deadline is Nov 30). In any event, you should have your scores by mid-Nov and thus can even wait to apply to the UCs then.
^^ Basically if they accept any test dates up until December it doesn’t really matter what you put on your application but what you send them from the official website. Although they will see all your scores, most colleges just focus on the highest composite score you receive.