I wouldn't count on being able to re-use the screen protector. It can be tricky to peel the skin off the screen protector without pulling up the screen protector (and risking the introduction of dust etc).
I tried it. The PS screen protector sticks really well and isn't really conducive to repetitive removals. The Element back is really sticky and will remove your PS screen protector.
Actually, the best set up I had was placing a SGP leather skin on top of the original plastic that was on the iPhone. That plastic stuck by static cling and therefore has been really easy to remove but sticks really well. So I have a PS screen protector and a leather skin that has the static cling plastic of the iPhone on the back. Very easy to shift around.