Would not expect any component changes unless the unit needed it. Given the unit was used the idea is just to let Bryston run the unit through their testing to make sure it was up to spec and there were no problems. Similar to the checkout and testing they do when they send a unit to audio advisor and it is offered as factory refreshed. James was asked about this in a thread some time ago.
Maybe, it the unit had a black dress plate, to change it over to the silver.