I recently had my windows professionally tinted in one of my cars. I asked if I could remove the tint later, specially the rear window. They told me, no problem, and they would not damage the window defroster. I think they mentioned a plastic bag or something. They charge less than $100 for it but, I do not know if that was for the whole car or the rear window only. Call one of those places and get a quote. Plus, if they scratch your window you have a NEW window!
Good luck
J.H.
86 300E