Can you drop tune a Floyd Rose?
You can tune to drop D using the fine tuners only, but if you want to go any lower you'll have to unlock the nut, tune, lock the nut, fix the trem springs to compensate the different tension, and repeat the process until it's tuned.
How do you lower the tuning on a Floyd Rose?
When tuning is complete, check the action of the strings off the neck. If your action is to high or to low, adjust the action with the two rocker screws (bridge pivot screws) using the 3mm Allen wrench. This adjustment will slightly change your tuning.