The add layout wizard in SiteAssist Pro asks you to specify what divs in your Sculptor layout to use for the menu, content, and footer. If you changed the Sculptor layout and removed or renamed any of these divs, that would break the SiteAssist Pro layout since those designated areas don't exist anymore. That is why it currently works like it does and requires that a new SiteAssist Pro layout be re-created. Its an interesting suggestion, but I am not sure we could account for the above scenario in an easy manner.