Hey Wesley, earlier today I updated the theme/page of my game--not the game it self. I don't want there to be a misunderstaning. I thought it was alright because of:
"The game itself must be made within the jam time period..."
Yes i'm pretty sure updating game page after the jam time is over is ok, i've done it for 4 gdevelop game jams and i never took any penalty of any sort.
As long as you're game is still in the jam, you're good. With itch, if you update the game file during the voting period of a jam, it will kick you from the jam, so if you made a mistake you would definitely have noticed. 馃槄