You are free to distribute modified versions of the code, again subject to the licence, but I also welcome patches to the code at my email address, ben@bellatrix.pcl.ox.ac.uk. If I choose to include these patches in a new dopewars version, you will of course be credited in the changelog (unless, of course, you don't want to be).
For information on the internal workings of the dopewars game code, and the client-server interface, the best documentation for the budding developer is the source code itself. I have endeavoured to add sufficient documentation to the source where necessary; any discussion here of the internal workings, however, may be incomplete, out of date, and possibly misleading. Feel free to email me at the address above with questions on this; I might possibly even know the answers!