If they aren't broke don't fix them... best advice I can give... and oh ya... run some diesel conditioner though your system, this is also good for cleaning injectors as well as the fuel system....
I would harbor a guess not any dealers are set up to actually refurbish diesel injectors. The would likely send them out to a diesel injector/pump rebuild shop for that. It takes much expensive specialty equipment for that.
In Seattle area we have Seattle Injector.
Maybe someone can recommend an outlet near you.
Usually one doesnt rebuild injectors unless theres a smoke problem not related to compression or timing, or a miss not related to compression or pump output. Or its stuck wide open.
PowerService fuel additive is good insurance.