Brakes and brushes are replaceable on most motors, separating the motor and gearbox is a no in most cases though!
Yep recommended to replace both board and motor depending on the year, iirc it’s about the magnets in the motors and saving the planet!
if you have spare carriages it will be easier just to swap the carriage out rather than pull the motor, I’ve done several under warranty when needed in the past due to company policy…
and factory motors don’t come with the pinion gear so you would need to swap that over
