When you say carbon fiber... are you refering to the comp tip of your mast? If this is the case than it is not really carbon fiber - just glass with some pigments in the resin. Repair... not having seen a pic I would repair the areas where the rivets have riped out with some resin (epoxy). I would not shorten the mast! You could also drill holes in your new part and the mast in areas that were not effected by the damage and rivet there. Kind of a odd damage - not sure why that happend. I would expect that the lager amount of force goes straight down. Check the general condition of your comptip... they age fast under UV light and heat - the whole thing might be ready for a replacement.

Patrick