I've got 2 Bandai Falcon's on the go,....one I'm building as the original Star Wars (ANH) version,....for that one I carved out the windows leaving just the frames,.....just using a sharp scalpel,...the plastic is pretty thin
My other one I'm building as TFA Falcon & because theres 'glass' in the CG model,...I built this one with the windows in:
To mask the glass I just used cheap masking tape.....what I did was,..press the tape onto the glass,...use your thumb to press the tape into the corners as best you can,....then use a cocktail stick to press down the tape right down to the edges & corners......then using a brand new scalpel blade, cut out the frames,...then remove the tape from the frames,....if any tape comes away from the glass,...press it right back down with the cocktail stick.....
Before spraying with primer,...give the part a blast of clear laquer,...this will fill any leaks in the paper with clear,...so when you paint with primer & paint it shouldn't seep under the masking tape,.....
....the main thing is, take your time,...practice on parts from your spares box,....
John