I saw a neat trick for reinforcing aircraft structure. This might apply.

1) wrap the spar with release film (wax paper, 2-3 layers)

2) right on spar build up your reinforcing sleeve from carbon/epoxy. Use an undamaged part of the spar for the mold Either vacuum bag it or squeeze out the excess epoxy. For a mast the sleeve would go a couple of inches above and below the damaged area and 3/4 around the mast. You would need 5-8 layers 5 oz cloth. You could probably use 10-layers of fiberglass

3) when hard, slide it off, square the edges and clear coat it.

4) Apply glue to the mast, slide the sleeve on and tape it down to dry. I would probably use a 1 part polyurethane glue (Gorilla Glue) I found this works best for carbon/Al bonds

This is for reinforcing, distributing a load, or just sealing a hole.