Hmm, interesting note you have there. First of all great work on RS- its my favorite mod by far
I have heard about the custom tile thing, and yes, so far as I see it, it is impossible to do so in Rome 2. However, I would think at designating custom tiles for each and every township would be a tremendous amount of work still (but I guess all that matters is the fact that it is possible).
I believe the method you guys use for minor settlements is Resources correct? Designate 3-4 depending on the culture and place them on the campaign map in descr_strat.
To Answer your question, there is a program I am using which would actually allow me to save the RGDV2 models into CAS. I have to say, however, I am not very talented in the whole model-texture thing. Only editing. But the program that I am using is a beta/demo and doesn't allow this function. If someone here is actually kind enough (or crazy enough) to make donations ~$80, I could convert them into CAS as you said. I am a college student and I am already spending way more money then I should be doing