No, not possible. RW is not an html editor; it is a WYSIWYG web design program. However, creating new navbars is not a major job. Recreating the styling of the site is not very hard and some of it can certainly be copied. I had a book website with specially styled pieces of text for the publication details. I copied the html straight into RW and the relevant CSS directly into RW’s site-wide CSS. To copy a site’s current appearance accurately, you really need a blank theme such as Foundation.
Having said that, moving a site to RW is a good opportunity/excuse to redesign it. I’ve redesigned this particular site at least three times since moving to RW, but it still has some of the original html. You can paste sections of html directly into html stacks (or the wonderful Scribe stacks).