Hi jbg - great to see you are active on Get Satisfaction - its a big part of how we track our customers needs.
As I mentioned in my answer to your idea about the ability to duplicate entire tests, it is currently possible to duplicate the champion variant of an existing page (and therefore get the opportunity to edit the url.)
To duplicate an existing page, just access the gear menu for that page on your Unbounce Dashboard (see attached image.)
If you want to change the URL for an existing page that is already published you can also just ask us to unpublish the page for you by sending an email with your account and page details to support@unbounce.com and we will be happy to help.
JM
