As straight & level has said, Polar operations on the 777 is very easy. In fact, off the top of my head I can’t think of one example where I needed to make the transfer in flight.
Just leave the Hdg ref in norm and leave LNAV to take care of the rest. The system is clever enough to switch between true and magnetic as required so no crew intervention is needed at any stage of flight.
Writing an SOP to force crews to manually switch between the two is in my opinion asking for trouble due to crew forgetting to switch back to norm and is actual dumbing down a very clever aircraft.