on any modern arm the COMM is epoxied onto the shaft so it does not twist!
so replacing the COMM is basically not worth any of the time and the windings will be loose and the motor will be totally unbalanced.
as far as winding goes its cake if you have the equipment. If not then good luck!
also most arms now have epoxy over the tabs where the wire solders on anyways, so they cant be unsoldered.
You can buy blank arms just contact the manufacturer.
also the wire used is special and the solder used is special and the epoxy used is special and unless you wanna spend 2000$ on a decent balancer then dont even waste your time.
But if you do get everything then winding is easy!
keys to watch for:
1=same number of turns per pole.
2=same wire tension
3=on any single pole no bare to bare wire contact (meaning any scratched or uninsulatd wire touching) cause it will short.
4=cleaned and prepped tabs for soldering
5=correct dipping epoxy
6=BALANCE
you can (but will suck) run an arm thats unbalanced but it will run like junk.
and also drilling is just as easy if not easier and more reliable then putty balancing.
this isnt meant to discourage but keep in mind that motor are delicate especially the balance so you might as well buy it from a professional.