Hmmmm well that'd most likely be up to the host of the contest (assuming Watchman is hosting it), but I'd say that as long as your taking something that's like a traditional folk type song (like marry had a little lamb or something) and adapting it to your own idea that'd be okay with me. As far as judging would go, that would probably either cause you to bomb in creativity or do very, very well in it (all depends on the judge and how you do it).
I'd say ask Watchman, but it's fine imo