Creative Assembly released a free map editor for Shogun 2. This is the first official tool released for any Total War game and hopefully is bringing us the future of support for this franchise.
If you wish to get it you can go to Steam and go to "Tools". This can let you create maps and these can be played in custom battles against AI and other enemies.
Rome 2 has recently been announced and is expected in 2013. A tool editor for this game is "harder" and they are not sure if they can release an editor for this, so enjoy it in Shogun 2!