One of my teachers had done this to his own mint Selmer Mark VI Bb soprano saxophone. Might have only been the altissimo palm keys, IIRC. Pretty sure he also did this to an ancient Conn Eb baritone saxophone that had key work from at least two different horns. He used cork and some sort of paper-y material.I do remember, however, that one of my clarinet professors in college back in the late 70's (Prof Fulginitti) played a selmer clarinet (series?) and he had added strips of blue electrical tape around the inside of the three exposed right-hand tone holes.
I asked him about it and he said that it made the clarinet play better in tune.
Any other similar experiences??