Regarding the defense you absolutely can change to a 3-4 during the season. I remember many years ago the Cards came out with a totally new 5-2 lineup they called the heavy jumbo or something similar. They dominated the LOS that game.
We've been a 3-4 team for years now, we can absolutely go back, remember when he was hired he very emphatically said he was not married to a 4-3, he understood we had been a 3-4 team since 07, were a top defense the last 3 years, and he wasn't necessarily going to change that. Obviously he has, but he said then he's coached both styles and isn't married to the 4-3.
If he's really doing what he said he was, evaluating everything, it's entirely possible to go back to a 3-4. Not saying he will, but he can.