There are some good suggestions in here -- however all of them are clumsy work-arounds at best (I realize something is better than nothing, though). The ability to modify, test, and publish is so fundamental to web development, it's hard to understand how this is missing. Also, renaming URLs can wreak havoc with page ranking and inbound links -- so that's not really a best practice. Having to copy all the content to a shadow page is also excessive work -- since there isn't a clone button yet either. When you go into edit mode, Squarespace should allow you to edit a shadow copy for testing.
