I uploaded my game yesterday, and a few people have pointed out that I should probably implement a level select feature. Can I still add this, even after a few people have rated my game?

I think I saw somewhere that Mark said that you can edit your gamepage, but you need to keep the build that was submitted and make it VERY CLEAR which one was submitted for game jam and should be rated. I'm not entirely sure about that though, so I wouldn't risk it.