Thanks for that question. I think it brings up some good discussion topics. Now, I'm no copyright lawyer so I may be wrong but I do take interest in these things. Sanity Studios will make every effort to protect its copyrights but fan work certainly helps to promote the hobby and would not (in my opinion) be grounds for litigation. For every copyrighted work (not just Sanity Studios') there is 'fair use' doctrine. Basically it is a few special exceptions to copyright. The four factors of fair use (wow, lots of f's in that last sentence) are:
# the purpose and character of the use;
# the nature of the copyrighted work;
# the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
# the effect of the use upon the potential market for or value of the copyrighted work.
(taken from wikipedia)
Basically if you make something for Bellicose as a fan and distribute it non-commercially, you 'should' be ok. We are always excited to see what players are doing. If you have other commercial partnership interests with Sanity Studios, you can contact us and we can talk.
As a note for fan products: Sanity Studios is a family company (or as much as mass battle game can be). Nudity, profanity, or excessive gore, while enjoyable to some, is not common for official Sanity Studios' products. You can, of course, make anything you choose but please use discretion.