Ran across this Facebook reel of a guy restoring a metal Studebaker pedal car. The way he replaced the "windshield" was interesting and could apply for scratched, dulled, or maybe even broken scale model glass, too. Instead of using a wood buck and a sheet or piece of new clear plastic, then sanding the edges to make it fit, use masking tape on the original and cut the tape at the edges to make a mask.. Then apply the tape to the new sheet and cut it out. Then warm and soften the plastic on a wood buck OR just flex it to shape while soft and avoid the need for a wood buck. The Idea of getting the piece's edge first, THEN shaping it to the frame seems like it would be simpler, but I have not tried it myself.
Maybe it is already well known method, but the pedal car video is worth watching just for the beauty of the guy's restoration even if the technique is not applicable in scale. Give the video a looksee to check how well the restoation turns out. Quite a diference.