It's been said that the luthier's credo is to "do nothing that can not be reversed". What does this mean? If an instrument is built poorly, and reworking certain parts will make it a better instrument, do we turn away from this work? Is regraduation always unethical? Are neck grafts that tweak the string length and/or overstand verboten? I've heard a lot about this "prime directive", especially from "holier than thou" luthiers who seem to have all the answers. I'm confused...help me, brothers and sisters.