If it is simply wiring up a new battery, this could feasibly be done by Thales/Securaplane employees supervised by Boeing staff. A revised algorithm or software tweek would be done and tested by the manufacturers.
Where it gets tricky is if we end up with a major redesign, where other parts of the system can't be tested before leaving Everett or Charleston because of a large chunk of the EE system missing awaiting FAA approval. :-(