What part of the phrase "take over retransmission" is escaping your grasp? D10 spot beams will become "the backup" to D12's spot beams. They cannot be active or they would interfere.And that has what to do with your claim that they are going to turn off the spot beams on D10?
The truth is more important than the party line. The documentation is clear and you don't need to subscribe to DIRECTV to grasp it. You do have to be interested the truth to appreciate the facts..