How far can this game be MODDED exactly?

Hi did anyone hear of a game called total annihlation.It is one of the most modded video games ever.It is extremely easy to mod and not only can you mod existing units but you can also ADD units too!I think the original versions had 400 units in total.Modders have ADDED 3,000 more units to the game!

Now back to topic:rome total war.Can Rome total war be modded like this.Can things be ADDED or can you only mod existing units and provinces?Like for example if I wanted to add North America to the map and make new provinces and new factions and add new factions to the game and not mod existing ones could I do that?

I used to play TA.I loved being able to download all those mods.Easy to install'em too*Sigh*Wish I still had a copy of the game.Going to have to pay E-Bay a visit.

On the modding fourm there is a list of limits