I just cut mine using a Dremel with the Perspex cutting disc. Had to cut it to suit fright train nacelle. I went to Clark rubber and bought a meter of slotted rubber gasket to cover the imperfections of the cut.  Looks fine now. 

Cut myself. Bought perspex blade for jigsaw. Put tape either side marked line to be cut sa not to scratch screen. Took about 5 min to cut. Then light gauge sand paper to sand edges

I regularly use these guys new screens, cuts etc  http://www.handcraftfibreglass.com.au/