Why would you want to play a different tactic in the second half for defense? I could understand wanting to change your defense after you saw what offence they were playing, but prior to the game you don't know what offence they will play.
Basically, defense changes should be due to influences during the game, for example if they are playing an outside offence and you are defending with a 2-3 zone then you probably want to change defence. But prior to the game there are no influences that would make you want to play 2 different defences like 3-2 zone and 2-3 zone at different points in the game.