Eek. I’d be afraid to try it, unless it was a harp on its last leg anyway or was no longer in playing condition.
I wonder if there is a way to transfer hand drawings onto a static decal, so it would be removable and wouldn’t directly touch the board. Something like this perhaps, though I’m off-the-cuff Googling. http://www.texascraft.com/hps/home.php?cat=253 Maybe a good art or printing supply store would have ideas. It would need to be flexible, waterproof, and not prone to chipping or gathering dirt. Somebody who makes harps might have other thoughts.