Hi Ed, Go ahead and unhitch the bass strings and string them on a piece of wire to keep them from running wild. No need to lower tension except on that you will unhitch. There is no danger to the plate at all unless it is already cracked. You can search the archives by using bass string removal or some such at http://www.ptg.org/archive/pianotech.php/ Good luck on the repair. Newton
This PTG archive page provided courtesy of Moy Piano Service, LLC