A friend of mine has a 82 trans am. When getting parts from the salvage yard, he took both front and rear fascia from a 88 trans am. For the newer pieces to fit, he had to modify the plastic honeycomb energy absorber on the steel bumper bar. Other than that, I believe it went pretty easy for the swap.
Unfortunately, for the 91 to 92 front end fascia, I can't say weather that would be an easy swap. Pontiac made some major stying changes with the 91 model, for the front end.
In the 3rd gen tech section there are exploded views from 82 to 02. These should help you see if the front fascia parts look to be a doable swap