Removal isn't too hard - you just need to figure out which is the right direction to push it. If it's been on there many years, you may need to employ a pair of expandable pliers.
Fitting has the small added problem of needing to push the clip down onto the post, compressing the rubber washer a fraction it they're new, while sliding it across. But at least it'll be clean and free to move.
All of this would be trivially easy on a bench. The problem is you've got to do it inside the door with very little access and all the important bits pointing away from you. To misquote Deep Purple, it is all done by the feel.