Our plan is to release our file-format information and expose as much of the data in the game as possible for you to extend and edit. We traditionally do not "hard-code" numbers so that our designers, and you, have the power to easily change and iterate on RPG data. We also plan on releasing localization tools to let communities around the world create localized versions for languages we are not translating Project Eternity into.
As we get more familiar with Unity during production, we will be extending Project Eternity even more for mod makers. Look forward to announcements in the months ahead as we make further progress and can provide you with more information about tools and mod support