Sorry John "I believe cabin crew have the ability to swap allocated seats quickly and easily using their Ipad in their hand"
Not correct.
The pax manifest held digitally at the departing station is the master doc and is a legal requirement. The crew ipad uploads from that, not in reverse. It serves for identification purposes in the event of "the sh1t really hitting the fan" and feeds into the weight and balance calcs (minor issue here on a 200 odd ton a/c)
The message is simple, do as you are bloody told or put on those Nike's and start walking.