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Yes, in itch.io game jams, you can further edit your game page as much as you like. (… and even delete your files, but not reupload them if the deadline is strict, so, careful!!)
(PS: not related, but using the opportunity: by the way, I ended up having almost no time to properly work on my game, so I only have a half-baked minigame prototype. ._. I am not submitting it, but I think I will test and review some games! And this was my first time dabbling in Game Boy development; I definitely think I will develop my game further, outside of the game jam. :) See you, people!)