I do not see how you can change the weatherstripping without taking the door off. The area needs to be cleaned and prepped for the new adhesive. Doing otherwise would be half-assed. Just take the door off. It really is not that much of a pain. Just 6 bolts. Once the door is off I would suggest a knotted wire wheel on an angle grinder to clean the door area up prior to repaint. Good luck.