This was an SP modification. When put in the "Commute" position, the switch put the switch gear into parallel so you started out in parallel and never had forward or backwards transition during acceleration and deceleration. In "Frt" you had forwards and backwards transition. After this modification, the engines were known as troublemakers because of not loading sometimes after making backwards transition, particularly the 3208. The "fix" was to zip the throttle to idle and then back out to what ever position you were in.

There was no HEP and no blended braking, unless you did it manually which was virtually unheard of in those days. The switch, being in the locomotive's electrical power system, had nothing to do with the air brakes.