I was wondering if it was ok to update screenshots and the front page of our submitted games without being disqualified? I've seen a few developers do this but I'm afraid to do this on my own. I just want to make sure!

Yes, it is fine. The only thing you cannot do is uploading or advertising a new version of the game (itch.io doesnt even let you)

What miracleJester said

I would avoid uploading images from new builds which don't represent what is in the demo. I'd like to show off some of my new stuff but have been avoiding it.