If I remember correctly, this is the replacement aircraft for the old EC-135C "Speckled Trout" avionics test bed. The EC-135C was retired several years ago and a KC-135R selected to replace it. The aircraft pictured is that aircraft.
I don't believe there was an MDS change as the new aircraft is still fully capable of air refueling whereas the EC-135C "Speckled Trout" had lost it's boom and had a command interior installed as it had a dual roles as the "Speckled Trout" and the aircraft of both the Secretary of the Air Force and the Air Force Chief of Staff. The new aircraft does not have this role, instead it is used for air refueling testing.
BTW, the little bump visible under the nose is the Honeywell Enhanced Vision System similar to that installed on many new high-dollar biz-jets. I think this will be an excellent addon to all of the USAF's transporters in the near future as it is much less expensive than a full-blown FLIR and it utilizes the already present HUD on the C-130Js and C-17s and which are included in the C-5M upgrades. The only aircraft requiring modification to their flight decks to accept the system will be the KC-135Rs.
Sweet, I'll get right on that one as soon as this semester is over. In regards to the EC-135R designation, I think that would sound cool but as far as the AF is concerned all references to this particular tail number designate it as a KC-135R. When they retired the speckled trout aircraft the 412th TW C/O referred to the incoming replacement as a "casey."