I'm curious about this as well, I'd like to touch up a few things but don't want to interfere with the judging or anything ( even if it isn't suuuper competitive).
However as far as I know, changing the page for the game shouldn't be a concern, just content in the game itself. If there's no answer from Kenney, I would say to keep the original jam build available and clearly marked as the jam entry, and then you can add new versions to your page. I'm definitely going to keep a jam build on the page for posterity :)