2002 100hp 4 stroke tilt/trim problem

Have a 2002 100hp 4 stroke. The electric tilt/trim motor has stopped working, and the motor is stuck in the down position. Solenoids tested OK, 12v measured across trim motor connections when up/down buttons pressed. Need to turn the manual release valve screw to lift the motor up, but this screw is a few inches below the waterline. Is it OK to turn the screw under the water, or should the boat be lifted out to do this? Also is it possible to replace the trim motor with the boat in the water?

[boats.net]

Should be able to turn manual tilt screw under water but can't replace trim motor unless it's out of the water.