Questions about publishing

I’m new to the VASSAL community and I’ve never published anything on the site before. I created an extension to the Betrayal at House on the Hill module for the Widow’s Walk expansion for personal use, but I have a few questions about posting it here. The first question is about permission. I didn’t get explicit permission from the publisher to make it or post it here, but the publisher isn’t on the banned list. Is there a copyright issue there? Secondly, where would I post it? Would I create a whole new page for the extension or would I add it to the page for the base game. Finally, the extension isn’t very good. It was made using poorly scanned and edited images. It’s certainly playable, but it’s not very clean when compared to the base game. Is that a problem?