The Creative Assembly has released the beta version of the Total War: Rome 2 Assembly Kit on Steam. These mod tools will grant players the chance to play around with textures, models, animations, and campaign-game starting points through the Tools section of the Steam client.
The Assembly Kit comes with example data, like naval vessels, soldiers, animation sets, and the complete Rome 2 database backend, with mod tools expected to come in the future. Completed mods can be uploaded directly to the Steam Workshop through the Rome 2 launcher. The game's Workshop page has received close to 1,000 submissions so far.
Further info, including instructions for installation, can be found on the Total War wiki.