Not everything can be stipulated in the rules... when in doubt, the commish is the ruling authority.
So what if the guy's been talking trash, it's part of the game.
FYI - there is a HUGE difference between a playoff bound team tanking to improve his playoff matchup and this nonsense.
The guy who is out of the playoffs... set his roster and lock his team. Easy solution. Have no regrets about this action.
However, I would be hesitant to touch the roster of someone in the playoffs... it could affect their matchups.
BTW - this is against your rules. As long as you have anything against collusion in your rules... this is multi-team collusion against 1 owner.
Lay down the hammer