The answer to that is, as you have noted: "It depends".
Say, for example, that you want everyone in the army to recruit either infantry or archers. Therefore you assign everyone who recruits MI to an army with orders to sit in the capital and do nothing. This would be a manner of excluding that player from actually participating and playing the game, merely for exercising his IR to choose his unit type.
If, however, a noble in a cavalry-only army ditched his cavalry and recruited infantry, moving him to your regular battle army would not be an issue.
This type of exclusionary behavior could be extended to just about any of the IRs. Assigning everyone who goes to a tournament to that "sit in the capital" army could also be an IR violation. I don't think I've ever seen anything like this actually happen, though.
