Oh I imagine for the physical parts and connectivity quite a bit of design and recertification work. But I'd expect the software that controls the refuelling to not change too much the aircraft S/W package already supports probe and drogue refuelling so I'd expect the boom control module s/w for the boom on the A to be replaced with the probe and drogue control module s/w used for the B. So the esting and integration regime should be somewhat less as it should be able to take the work already done for the B and C.