If the coach can change defense he should be able to change the offense too.
If he only could change the defense this would become an ebay game where teams would chase the best defenders...
???
On current game-definitions, the coach replace the defence and the offence every TO.
I agree that having also a secondary offence will be a good idea as well.
Letting the game be less random (letting the coach decide to what will be played after TO) is always a blessing.