Well, the X-acto trick is well known but might not work always. Be shure to cut the finish along the side walls of the nut, then tap lightly
front to back and vice versa. Use your fingers when it starts go let go. You might be able to slide it out sideways with pliers if yoy loosened it enough. A better way might be to cut it with a thin saw along the nut length, almost way down to wood and then collapse it towards the middle.
This will save the finish 100% if you are careful, but be shure to cut the laquer first and protect head with low stick tape all over.