I don't know if it's allowed, and the rule page on tumblr doesn't specify. I would like to be able to update my game after the jam, but it's alright if it's not allowed

i don't see the reason why you would be forbidden to update your game after the gamejam, tough if you wanna be extra careful you could just make another project with the updated game and keep the final version used for the jam in the original project you provided

Yes, you can update game after jam's ending.

This has been answered on the FAQ; 

• Can I update my game after I’ve submitted it?

Yes! You can update your game after submitting it–even after the jam.

Please put your questions on the FAQ thread in the future.