Tasty this change is awesome.
I cheated and got an admin to unanchor the piano for me, so I was dragging it around the station playing Still Alive while the AI and a nuke team were wreaking havoc around me.
It was beautiful.
I do think normal players should be able to unanchor and move the piano without admin intervention, though.
Also, usually the tempo detected by midi2piano, and the tempo actually needed in-game for the song to sound remotely right would be way off. For instance, say the tempo of a song is 120, midi2piano might detect it as 171, and ingame it would need to be played at 240 to sound decent.
Other than that, it's really cool, and if it weren't for all the lag spikes and stuff in game due to all the processing, it would probably sound great.