Hey Sean, some of the boats I have split the hull on has had a thin over-lay of glass on the inside of the seam, I don't believe it's anything to do with structural integrity, I believe it's a preventative measure to keep water from sneaking up thru the railing and into the boat. What I have seen is about a 6 ounce mat, and I've easilly cut thru it with a sharpened steel putty knife, and I have used an old butcher knife persuaded with a small ball peen.
and Yes, alot of these boats can be re-structured with-out seperating the hull, but in some .. like Mine .. it sure made the job a lot easier for me to do it.