gunswizard,
Forty years ago many fishing rods were built with the rod blank stopping just inside the handle so the inside of the cork grip will make a difference in making a repair.
I replaced a cork handle once having to remove all the rod's guides and cut the existing cork off the rod blank. Doing so was a pain in the ass but a labor of love.
Curious as to the make of the fishing rod you want repaired.
Doc
Handle replacement can be done without removing the guides. Ream the handle out so it will slide on from the butt end. Then wrap the blank with thread so you get a tight fit at the front of the grip. Once the front of the grip is tightly fitted simply fill the grip with liquid epoxy from the rear.
If weight is a concern you can build up the blank with thread in just a couple spots and apply epoxy to just those couple points. I would only do this on rods that are going to see light use.
If the rod blank does not extend through the handle all is not lost. Most any builder will have scraps of blank on hand and can easily extend the blank through the handle.