I have some bass pro shop carbon fury 4560 arrows with blazer vain that are 3 degree offset. I was wanting to know could, I cut them down to make some 20 inch crossbow bolts.
You can certainly cut them down but first you need to make sure that the spine weight is strong enough for a crossbow arrow. If they are comparably to a Goldtip Laser II they will be okay.
Most crossbows require a 21-22-23 series shaft diameter. The shaft must be big enough in diameter to sit on the groove in the rail and be centered by the string on the nock end!!!
If those are small diameter carbons they will not work with most crossbows. The string could jump over the end of the shaft when you shoot.