Maybe it's just the picture making those hinges look fatter than the ones I used. Lengthwise you'll be fine cutting them down as long as you still have a couple of barbs inside the control surface to grip onto that epoxy with. Obviously you should keep them as long as you can though I used a drill press when I was drilling the holes into the ailerons so that I could get the holes as deep as possible without puncturing the surface (it's a little tricky as the ailerons are tapered, so take your time and be careful when you're doing it. I would also strongly recommend making a drilling jig for the ailerons/trailing edge so that you guarantee hinge alignment.)

Cheers,
Neil.