To Battle! Empire & Napoleon Made Moddable 

A source of what could gently be called discontent amongst the Total War community of late has been the lack of modding tools for the most recent games. Empire, Napoleon and Total War have all been bereft of official utilities to alter and add units, maps et al, which was partly a result of the relevant files being compressed and thus tricky to edit. At last, the Creative Assembly have found a way to open things up a little more - releasing the complete, original, unpacked raw database XML (data from tables) and XSD (table structure and field properties) files for both Empire and Napoleon.

Which is, essentially, what modders have been waiting long years for. No sign of Shogun yet, but hopefully it's incoming. The Total War games have a long, proud history of both minor mods and total conversions, and seeing what the most recent versions can be turned to will be a whole lot of fun.

The full CA statement is here, and in theory the files you need are here, though the link appears to be dead at the time of writing. Hopefully that'll be fixed soon.