First off, Let me just say, I have never shaped a board so I have no experience in any step of the process. I am an experienced wood worker, so I'm not an idiot, but I wanna know some opinions/stories about the topic.

I have this old 8'0 Brian Heritage funshape, that is about as fun as stepping in dog ****. Its got a thruster fin set up with a pulled in squash tail. I rode it for the first time today after many years, and realized I wanna cut the tail off and make it a thick roundtail single fin, length in the 6'6 range.

All the research I have done, instruct you to de-lam the entire board. Question is, is there anyway to save the Fiberglass, and just glass over the tail portion that is reshaped? Also, I would like to cut a finbox for the single fin, Is it recommended to route out the existing fiberglass for the finbox, or to re-glass the entire section?