What possible motive would S31 have for over-riding the pre-programmed sequence?
To do some research? Kirk and Company knew they had the SS Botany Bay before ever going over. Section 31 would've likely did all the investigative work about the ship before beaming over and dug deep to learn everything they could about the passengers and ship, including how the control the cryogenic process.
I think that the intention of the writers is that Cumberbatch is Khan. But I think they intentionally left themselves some wiggle room.