It is possible to create named characters in the faction generals and captains, each with different traits that can be modified. Total War is surprisingly good for roleplaying characters, and can be modified further to have more impact. I don't know if the general's models themselves can be made unique for each character (they could in Alexander.) It would be grand to have Conan, Trocero, Pallantides and Prospero charging against the pitiful Nemedian spearmen!

I've been in contact with Dale himself regarding the mod: he basically suggested that for things like characters and city names I should refer to existing material (so I'll probably go back to Haloga and Sigtona for Hyperborea) or, if none exist, then make up my own.

The magic of the Hyborian Age could be replicated in Medieval, since it basically comes in a few types:

Mentalism = this is things like hypnosis, brainwashing, and similar mind-altering techniques. This is easily replicated using morale traits and flags.
Black Plagues = a popular form of assassination used by Stygians and Acheronians, where they cause a black wind to storm through a populace and kill anything they touch in minutes. This is a bit of a problem, perhaps it would be more practical on the strategic map through triggers.
Summoning = the art of summoning and controlling eldritch beings from the Outer Dark. Hopefully I'll be able to include classic Howardian beasties such as his ghouls, great apes, giant serpents, Children of the Night and Devils from the Outer Dark. This last one will be the most terrifying unit on the battlefield, and hopefully the most impressive looking as I have some interesting ideas on how it could be portrayed.
Awesome Cosmic Power = this is displayed by extremely powerful sorcerers like Xaltotun and Thugra Khotan, who can rock the foundations of the battlefield itself by causing earthquakes and explosions. I'm not sure how best to show this, as using fireballs and the like seems a bit blunt. In any case, a sufficiently powerful sorcerer should cause more destruction than a full stack of Monster Bombards.

I'll be posting another update soon: as a change of pace, I'll show some of the new buildings that will (hopefully) appear in the mod!