I have (cough!) more than one EMG - equipped bass, and have played around with their configuration for decades.
The pickups themselves are resin potted, so not repairable as you'd have to destroy it to get inside. I've always worked on the principle that backup extends to warranty replacement of a new pickup, or you're on your own ie source a replacement yourself. A rewind isn't going to happen. Pots and switches are easy to obtain, either 'official' or off the shelf at electronics outlets.
Touch wood, I've never had an EMG pickup fail in the approx 30 years I've had a variety of them. :-)