Mark: You don't " Compress " the frizzen spring to remove it. You let the frizzen compress it, and then simply put a clamp on the spring to hold that position while the frizzen is opened, taking the pressure off the spring. Then its removed. I remove frizzen springs all the time to work on polishing the contact spot,( remove rust when someone hasn't kept it cleaned and oiled) and to remove the frizzen so that I can correct the shape of and polish the cam, or " heel" of the frizzen, which is what compressed the frizzen spring when the frizzen is closed. Once the corrective work is done, the lock and frizzen spring are cleaned, burrs removed if they are rubbing against the lock plate, then its oiled, and reassembled.
After that work is done, only regular maintenance and oiling is necessary. Done correctly, the springs don't break. Let some garage gorilla decided to compress that spring with pliers, and yeah, he's going to break springs.