I was able to take one apart and save the rivet by using pliers around one end to smash the peened end back down to where it would fit through the hole. I've done it exactly one time so don't know how repeatable it is, and it took some time. I think a pair of
bird banding pliers would make it easy, but who has a pair of those lying around? If you can find proper replacement rivets, that would be the way to go. I couldn't, so wanted to salvage the existing rivet if I could. But the rivets themselves are soft and the peened edge can easily be ground off with a 2" roloc disc on an angle grinder. Just did that last night on a handle I was using for spare parts.
BTW, those GT handles remind me of the old backpacking joke of drilling holes in your toothbrush handle to save weight.