I'm having alot of fun with this mod playing as the Germans with the Rampaging Barbarians option set. One thing I find myself reluctant to do is to upgrade them because then they are no longer Barbarians. Would it be possible to set it up so that they upgrade within their internal hierarchy as you gain the appropriate technologies? With the exception of the special unit the Landsknecht, 'cause they're way cooler than regular Pikemen. Though I guess if I want them to be able to become Landsknechts, there's probably no way to remember that they were first Barbarians and upgrade back into that tree. Darn.
That would be possible I reckon. You have the barbarian unit upgrade to another barbarian unit instead of a regular unit, and have the cost at -1 so you can't build them