Thinking back, I won't say now that the entire assembly has to come out. When I did mine I had the doors off the car and everything stripped out. That made it easy to work on each piece.
You can install the rubber without removing anything but you do have to cut the rubber where it goes around the top hinge and bottom pivot post.. If you're replacing the rivet you can do the rubber without cutting anything when you pull the window out.
Getting the glass out isn't always easy because the pivot post might not want to pull out of the tensioning plate inside the door. This is two plates held together with two bolts and is fitted around the pivot to provide enough friction to keep the vent from flapping around on its own. You'll also have the problem of getting the post back in to this plate, unless you pull the door panel and can reach up inside the door to adjust it.
Also, mashing down a rivet is nearly impossible while the window is on the car. Wolfsburg West has a correct rivet ( http://www.wolfsburgwest.com/cart/Detai … ID=N136612 ) if you can't find something suitable at the hardware store.
You can do the job on the car; if I was doing it again I'd take the whole frame assembly out.
David H
'66 VW Beetle w/sunroof
http://tinyurl.com/qhw59"Where am I going ... and why am I in this handbasket?"