Jr. High school teacher in "Shop" class said never use a screwdriver as a pry bar. But he isn’t watching. Try to re-create the original shape as you work it off with the forbidden screwdriver.
I assume you are trying to save the uber-expensive clampscrews. Be careful how you get those retainers off or you will mess up the groove in the screw.
It took me a while, but I finally found this diagram that Garry had provided to me some years back. There was a special tool, or block really, that was used to, I believe, un-flatten and then extract them. I think when I did this to a motor a few years back I used a simple block of wood with some degree of success.
I pry them off, cut the nub off, then drill & tap them for a bolt. I use a 1-inch 1/4-20 bolt and thin the hex head down a bit on the grinder (so it doesn’t extend beyond the cup washer). I drill in about an inch into the thumbscrew. I then run a tapered tap in until it bottoms out. That leaves the last 1/4 inch or so of threads not quite perfect, which is perfect for burying the bolt into them so it won’t back out. Make sure you don’t run the bolt in deep enough to clamp against the cup washer as you still want it to be able to move. Not original, but they hold better than the clips and can be undone easily later if you bugger hip a handle…