No one is suggesting a complete overhaul. It could be a very subtle change of attacking structure, a quick switch in defence or a new target of the opposition.
I remember one game in 2011 (although can't recall the opposition) where we lost out left side centre and backrower early in the second half and resulted in Prior defending wide, so the opposition sent several waves down that side and ran in 2 tries to bring the scores very close. So Bennett sent the message out with 15-20 minutes to go for Hornby to move 2 defender out and cover the centres while Prior defended at 3 and boom, the attack was thwarted. Simple, easy Plan B.
These days, Fox Commentators come out after half time and give an update of what the coaches told their team in the shed. Some of them are useless, but many of them indicate a subtle shift in play - target a certain area of the field, Player X needs more early ball, start switching the play back inside or kicking early, this sort of thing. THIS is what we refer to as a Plan B, the ability to adapt to in-game situations. I distinctly remember the Warriors game where Mary's half time message was 'just complete your sets' even though anyone remotely familiar with Rugby League could see that our game plan wasnt working, and when I think of that I cant identify any tactical or strategic messages that he employs, always generic cliches (similar to Price's famous 'run hard, tackle hard' plan). This is an area he needs to either improve or recognise his deficiencies and outsource.