Just what do you think they do when they "remanufacture" an alternator?
The old alternator is torn down to its constituent parts. The parts are inspected/tested and cleaned. Reman alternators are assembled from the old pieces (probably no reman ends up with any of the same pieces as before). Except for brushes and maybe bearings, the only new parts are to make up for shortfall when there are not enough old pieces. Occasionally, new or rebuilt rotors, stators, rectifier plates, or voltage regulators may be used.
Part of the process may include resurfacing the brush slip rings on the rotor. If it needs more than a gentle resurface, the entire rotor is usually scrapped.
Personally, I would rather go through my own alternator and actually replace it only if it needed expensive parts. You know its history (which you don't for the many components going into the reman).