Personally, I wouldn't even think of touching a thing. If Fred wrote it I would want it all original. Anything that you do to take away from original condition, including Fred's writings, would take away from potential collector value as well as destroy a small piece of archery history.
Just my opinion, but I would be proud to own a bow signed to Big Al if it was written by Fred - regardless of who Big Al is. The only way it could be better is if Fred had signed it to you personally, but of course that didn't happen, and deleting the writing can't alter history. And if Big Al turns out to be Al Reader, you have a real treasure!