I play a Fender American Deluxe Strat with Fender/Schaller locking tuners. I'm assuming that the Schallers will be similar to the Sperzels. To string the axe, you loosen a thumb screw on the bottom of the key, pull the string through and tighten the thumbscrew. I then tune to pitch, stretch the strings and retune. There is no problem tuning to a drop D or other and returning to E. However, if you have a locking nut - these usually require loosening with an allen wrench for string replacement. Fine tuning is done at the bridge. I don't know if the tuners have the range to tune down to a D or not.