As former Car foreman on Bombardier Equipment, I can tell you that changing the phasing of Hep circuit takes all of maybe 2 hours per car.
The HEP receptacles are all joined in one single connection box under center of the car.
By switching the cables from A phase to B phase the rotation is reversed and conversion complete.
The Wof H fleet does need all door key switches and locks replaced , a job that takes a lot longer,however since NJT uses differed door keys than MNCR.