I've got a ''90 7 Up 'vert with water in the RH side headlight. Every how to on putting in a new head light removes all 3 lights, head, turn, and fog.
Is this really necessary? Has anyone done just headlight remove and replace?

 

Sorry I dont have the full answer you are looking for. I have replaced mine but its been a while. But I do know that I changed all mine and it only took 30-45 minutes for both sides.

Also it may look funny just changing the center piece if the others are old. Just some food for thought.

 

That fast? I'll take your estimate and triple it, I don't move as quick as I used to. My 7 UP has been garaged it's whole life. The lights are like new, no hazing or scratches.

 

To answer your question Yes you can remove the head light housing without removing the turn signal and side marker light however the rubber stripping around the headlight housing is going to make it a pain to put back in but it can be done.
If you plan on replacing the head light housing I would recommend replacing all of them as one new housing will be VERY noticeable against all the others regardless if you've garaged it or not.

Good Luck!!