I've never worked with carbon fiber but work with fiberglass all the time (I restore Corvettes for a living) and I'd suggest the very fine toothed saw approach, such as a hack saw using a 32 tooth per inch blade, which is made to cut thin wall tubing or pipe. A better option might be to buy a coping saw & blade meant to cut ceramic tiles. There is a blade that in actual fact is more of a file than a toothed blade, so it won't shred the fibers. Before making the cut I'd use the tape trick, wrapped tightly to both protect & act as the guide, cutting right next to it. I'd also only cut part way through rocking along the side of the tape as far forward & backward from the top as is easily done, going all the way around by rotating the part as necessary, and continue doing this until through. After that I'd use a very fine sandpaper, preferable a wet & dry type around 360-400 grit with soapy water to sand & smooth the area with a slight radius (or bevel) to the end, inside & out. That should prevent any issues with chipping, fraying, or rough edges. If you go with the fine hack saw blade go slowly & do it the same way I suggested for the coping saw. USE LIGHT PRESSURE on the blade, don't rush it.