Hi

I think the windshield is reusable when retrofitting the flush trim. The old non flush trim is secured to the glass by clips - there are a lot of them I suppose. Remove them and let a shop install the flush trim on the windshield.
You should only be very careful not to damage the windshield when removing the old trim and those clips.

If your car is a wagon the whole tailgate has to be replaced when retrofitting the 90+ style rear window, because on later models with flush glass,the window opening is somehow different. The 90+ tailgate will fit without problems, only the hose to the washer nozzle has to be rerouted, given that the 90+ have the nozzle mounted on top of the gate.

If you have the sedan I don´t know if the rear window could be modified in any way.

Good luck and lots of greetings

Ciao M.P.