There usually isn't much warning when a carbon shaft goes. I stump shoot just about every morning, mixed in with target shooting. I stump shoot with a carbon arrow with a judo head, because it lasts longer than wood or aluminum. I have had a number of times when a carbon arrow fractures at random places along the shaft, a lot of times just in front of the fletching. I think this happens because there are a fair amount of side impacts when stump shooting, which starts a fracture, and then the fracture breaks under the stress of being shot. I have seen pictures of what happens when a fractured carbon shaft penetrates a shooter's hand, and it isn't pretty. I flex the shafts pretty often, and that catches some of them, but not all of them.
I guess this is a long way of saying that I wouldn't want to do anything to a carbon shaft to make it weaker than it already is, particularly on the nock end.