Can headliner be installed with glass in?

No , but it is much easier. There are serrated edges at the top of the front and rear glass that "bite" into the headliner to keep it in place. Unfortunately they are very close to the rubber gasket and makes maneuvering and tucking harder. As well , on the fastback model anyway, there are two tensioning springs to keep the headliner taut. I've done it both ways and it is way easier without the glass, seats, and overhead trim in the way!!