That sounds reasonable to me. I didn't even think about building for windows since I'm mostly on quest and now I feel sort of silly about it

Generally speaking we don't enforce any strict rules here atm. If you find a bug, or are able to add a platform to your exports, sure go ahead and add them in. Just be upfront about it and do an update on your devlog page or in a comment in your project.

Big changes are frowned upon, if you're planning to keep working on your project after the jam it's better to wait until the voting is past before uploading big changes.