Quote Originally Posted by Vider
I believe the correct answer was stated above, that it was corrected in a patch. I am currently playing unmodded MTW (with VI expansion) and I'm in the process of retraining Early royals to High royals. I think the royals are the only ones this works with though. My fyrdmen and viking huscarls are simply merged to replenish them.
Okay, well then I do stand corrected. (Like I said, it's been a good while since I played the vanilla game.) As for Fyrdmen, Huscarles, Varangian Guards, and other units that are exclusive to the Early period, there really isn't anything you can do one your game enters the High period. Aside from "cannibalizing" units of the same type (such as what you described), there's really no way of replenishing period-specific troops.