I hope this get's locked soon.
Timeouts would be a great place to effect the tactic changes.
To make it clearer: you would set before the game: take timeout in minute 15 and switch offense to run and gun and defense to 3-2 zone.
I like your idea of adding situational tactics to the game. I remember a hockey manager game which had these features and I thought it was fun. You could set things like "Pull your goalie for a sixth attacker when down by less than X goals and with less than X minutes to play" or "Play a defensive game when ahead by at least X goals". Yes, it was rather complicated for a newcomer but the fact is that you were not forced to set these advanced tactics, you could just let the AI take all the decisions and still had a fair chance at winning the game.
I think you overrate the offensive ability to score. A good percentage to score in a season is what? 50-55%. Even the best players of the world don't have better stats that that.