Don't know how to take off the spool on a cannon. It probably comes off the spindle with a nut or something pretty easy though but can also cut the wire out in place with with some stout wire cutters and go back with new. The old stuff now has, and as you most likely know, undoubtedly has some permanent'ish kinks in it to that'll just make life tougher down the road........i.e., it'll be catching itself as it pays out.
So different topic but, relating to birds nests and the like........
Have you tried to run braid? I spooled one rigger up this fall and ran it, seemed to run okay through the water but one thing I didn't like, well two, the $$price$$ to benefit/s gain wasn't all that tremendous, non that smacked me in the head anyway. And it tended to bunch up on itself paying in and then sometimes fall off its bunching hump ( I made that up for lack of a better term) creating loose loops in amongst the normal tighter coils........
Then when paying out with loose loops, when a loose loop when come around, the weight would of course drop fairly rapidly snapping out the slack these loose loops made..........I took it off after a few trips