So what if you could have 1 tactic in advance to second half - if you are losing the game? Like you lose 45-55, playing low post against 2-3 zone (well obviously coach should know that during that time), you instructed your coach to play RaG (or better outside isolation, because probably there will be only like 1 outside player capable to do anything about it). Or maybe you could switch a whole lineup.
but if you react normaly the oponent react too, or not especially when the changes are drastic. Today the coach adjust the tactic slightly, when you play outside against an very strong outside tactic you play more inside later in the game, and if that is working the opponent coach maybe starts to protect his basket better. The same goes for 2-3 Zones against inside tactic, that the focus starts moving outside currently - but in a way that the right tactics from the beginning are always better.
I think with such drastic changes tactics starts to become unimportant, and people maybe even starts to complain that they loose because trhey scored 5 points to much in the first half ;)