No problem carbon is easy to cut with a rotary tool like a dremel or with a very fine-tooth saw (like a metal cutting hacksaw). Its important not to use a saw with coarse teeth, or you’ll rip out fibers along the inside of the tube.
Make very sure you “measure twice and cut once”. Use masking tape or something similar to mark off the area to cut an then go slow to make sure you’re cutting straight.
Use some 150-200 grit sandpaper to smooth off the edges.
Its easier than you think, good luck!