Of course there are actually always a few people that like to upload early to get more feedback and then update it over the rest of the time. You can reupload and therefore also update your game as long as the jam period has not ended.
I've never thought of uploading early as a type of Early Access! Very clever. I just wish I could work fast enough to have something playable that early.
Yes! You can update the game after uploading it, even past the jam date! The point of the jam is to learn, so if you want to continue updating your game after the jam ends you're completely free to do so. Just know that most people will be looking to play games after the jam ends.
