It's posible, but i don't know how. I think there's a guy who moded the movement posting in the Progression thread. If no one will answer you you can ask him.

However i don't believe this would add realism to your game... The AI could do some wierd stuff. For example Carthage could have Italy overrun in a turn, without the romans even noticing it (bad if i assume you would play with rome), or any other wierd action. Like a huge army landing in the peleponessus, even if you had a navy stronger than your opponent, since you wouldn't be able to prevent the landing.

That seems kinda unrealistic