It`s something personally I`d cautious of doing for fear of ruining the overall `look`of the system.... guys can and do cut partials from stocks, but they`re usually strips which sit at the front hairline area.... a custom will have been made to the size and shape [contour] of your head from your template with the hair ventilated in such a way so as to lie like a full head of hair on top..if you were to shorten it by cutting a strip off the back the results are unpredictable...putting it simply-- growing hair will grow back eventually if/when cut but once a system is cut that`s it.... experienced guys experiment a bit with old systems but as a new wearer and on your first system, I`d say leave well alone..you`ll have enough to cope with with doing bonds etc. without opening another can of worms for yourself.....just my 2-cents worth ! Regards.