Shutting down half the aircraft's AC electrics, even for a short time, would be a major step to take, with serious repurcussions
In light of the actions taking place aboard 9M-MRO at that time, I wouldn't think repercussions from de-powering the left Bus and the left FMS would be of much consequence to a person in the act of diverting the plane from its scheduled flight path.
I'd be very surprised if a pilot would do that deliberately just to interrupt the satcom system.
I don't think it was done to disable the sat system - in fact I believe that was an unknown and unintended consequence of de-powering the left AC Bus. IMO the bus was taken down to de-power the left FMS which would allow direct pilot control of the aircraft without interference from the FMS. The FMS would provide physical resistance to control column movements which are outside those Boeing expects an airliner to experience in "normal operation."
There are far easier ways of disabling the ACARS & satcom if that was the intent
There is no other way to disable the satellite transmitter/modem from the flight deck other than to de-power the left AC Bus. The CB's for this are in the EE Bay.