I might have missed it, but is the major wiring issue in the operation of the train, or in the hotel services.
If it is just affecting latter, the passenger comfort, toilets and displays etc. And there is no problem operating a train, then it would be possible to hand over a few for driver training, so can train the crews whilst others are updated and fixed. Once a few are in service the training units then go back for modification.
The very long 701 Introduction thread mentions about 6-8 units passed for training, but not fully updated to passenger carrying condition, so could similar happen with 810s