Tamar,
I have cut and shut windows on many standard cars to save a few grams. Vac forming over the top of the original piece and then cutting and glueing the windows back in place individually saves more weight and retains the standard look...again I have done that several times now.
I suggest it would take an eagle eyed judge to detect the difference.
Grinding or cutting the centre section out of the original piece can lead to cracks and breakage....ask me how I know.
Who is shooting anyway?