Yes there is a case, when your whole realm believes that you (leader) requesting people to get infantry instead of archers is great, and the ones been requested are happy because their General/Marshals contacted them privately requesting them something and feel great about been able to help the realm other than just moving. There you go, a perfect example.
This is a perfect example of ... nothing. There are demonstrated and proven ways to encourage unit type selection out of your nobility without breaking the rules. I understand that Sirion does this quite well. Perdan does this effectively (or, did while I was there, and I think they probably still do), and Darka did, too. When I was general of Darka, I received a few messages from rival generals asking how we got nearly all of our nobles to lead infantry, instead of archers/cavalry. In Perdan and Darka, we did it 100% legitimately, without violating any IRs.
You *can* provide guidance and influence the choices your nobles make without violating the IRs.
* Sending general messages to the realm stating that it would be best if the army was 2/3rds inf and 1/3 archers as opposed to the 50/50 split it is now, is OK.
* Offering a 300 gold bonus for every archer leader that dumps his unit and recruits infantry is OK.
* Offering a 50 gold/week or 100 gold/refit subsidy for every infantry unit is OK.
* Sending generic realm-wide or army-wide messages stating the armies need more infantry is OK.
* Sending personal requests to individual archer leaders asking/telling them to switch to infantry ... not OK. (Unless they PMed you firs,t asking for recommendations on unit type. If they ask you first, then you are free to make personal recommendations.)
I cannot stress enough that it is absolutely possible to be a general/marshal and
never break the IRs. There is never a valid reason to break the IRs. Period. If you think that breaking the IRs from time to time is a requirement of being a good general, then you just reinforce how, IMNSHO, a realm-wide warning was absolutely appropriate.