As far as I remember, from Empire onwards it's no longer possible to mod the map (amogst other important things) on TW games, that alone makes TCs impossible. I remember reading an interview on TWC where they justified this with the "GAME IS NOW SO COMPLEX, YOU CANT MOD IT" sort of point. This was on Napoleon times.
For mor information about the matter go to TWC forums and peek a little trough the modding section .
It looks like it actually is possible to change the world map but it's much more difficult than it was in pre-Empire games.
I'd have thought that would have been supported by the Assembly Kit, but it's not. So I guess I was wrong, older TW games were, in fact, more mod-friendly. That's pretty disappointing
CA took a very anti-mod attitude after Medieval 2, its quite depressing because mods are what made Total war games what they are. Europa Barbarorum, for example, is proof of what a dedicated team can do to a game when the game gives them a chance. In spite of how many sales that cost them.
Here is the worse part of all this, they lied constantly about it.. When Empire was released CA lied CONSTANTLY about mod tools, they swore up, down, and to the left that they would release modtools asap and a huge amount of people believed them and bought Empire because of that False-Promise. They STILL haven't delivered. Now Empire's modders have done a whole lot considering how limited they are but because of CA not making Empire moddable and not delivering the mod tools they promised its a lot less then it could be.
In fact even if CA decided to abandon their anti-mod stance and allowed modding fully, their attitude toward mods from Empire onward has essentially killed the modding community, sure, sure, there is some diehards but it is nowhere near the amount of modders total war had in the past.
They did apparently release some mod tools for Shogun 2 but from what I've seen it was pretty much for Multiplayer maps. (Though it seems from your link, the modders being as resourceful as they are, are bending it to their will, which is good.)
Honestly though, these days I realize, that if your game can't stand on its own without mods, its not really a good game, and Total war games
cannot stand on their own, even tiny amount of things people can mod in Empire is required to make the game playable, same with shogun 2. (Though for me shogun 2 is such a piece of shit that not even darthmod can make it playable for me)
Sorry, for dragging this off topic, Total war games used to be an amazing series with amazing mods and CA killed that, so I kinda have to rant about them sometimes.