Singleplayer? Singleplayer!! Dude, get into some multi action, the AI could never hope to be a match for you
Maybe the hero-mod should be divided into three parts, so that there's one for each era. That would allow for modifying the units directly, which could come in handy in cases like the Eagle Priest and the Couatl.
(A further example of a possible inconsistency would be Late Age T'ien C'hi's heroes: Seems to me they are the same as the other Ages, which doesn't necessarily make sense given that the old nation has been subjugated by barbarians. Why would the heroes of old aid the invaders?)