Nah, you've done that wrong mate. I'm not at my OMSI PC at the moment to refer, but I can tell you that Page 73 onwards of the English SDK manual tells you exactly how to do what you're trying to do. I set up a 'D92 only' AI group for my Dannenburg map and works fine.
You don't change the main AI list, you just add a new entry, then select that new AI group in your new route.
Cheers,
David.