How do these come apart to swap out the seals? I assume the pin has to be yanked out - no luck with that so far. Can't see it being a bid seal if I just cut it off flush to the post. What bout the small screw ... is that an allen head or flat blade? If allen head, what size ??

Yes pull out the pin , if you cut it off flush how are you going to reinstall another so it doesn't it designed job ?

As far as that screw ??? I think that whole frame that is chromed is cast as 1 piece ?

Screw hole is for the top of the door weatherstrip.
Black Phillips-head screw.
I've found strip caulking under the weatherstrip in that area on original cars.

Here is a step by step article on how to restore the vent wing assembly. It should be a great help. https://moparconnectionmagazine.com/gallery-how-to-restore-a-vent-wing-assembly-with-door-glass/