No, you cant mod Total War: Warhammer.

As both a Total War fan and a fan of Warhammer, I can stand tall and say that yes, yes I am ready for Total War: Warhammer. I can also say that I have worked tirelessly to separate fact from fiction, from what is confirmed and what might be confirmed soon.

Alas, it is my heavy and solemn duty to inform my fellow Sons of Sigmar that Total War: Warhammer will not allow you to mod it.

You cant replace Dragons with Thomas the Train engines. You cant replace the face of every Ork with that of the Macho Man Randy Savage. You can not add in your own custom factions, your own custom nations or plots or ideas. You take it the way they make it. Do I blame Creative Assembly, the creators of the Total War franchise? No I blame Games Workshop, the creators of Warhammer Fantasy and its 40k counterpart. They tried to claim exclusive ownership of the term "Space Marine". They sued a woman who self-published a book called "Spots the Space Marine" because they said that they owned the term "Space Marine". Seriously, look it up I'm not kidding. More bad news includes (but is not limited to):

-No family tree.
-No naval combat, it's auto resolved.
-No Chaos faction at the moment.

Indeed, these are dark times for the Warhammer fanboy. But Creative Assembly has a long history of creating quality games and if the gameplay I have seen so far is going to be anything like the end result, then I am confident that we're looking at a triumph for the limping Warhammer franchise.