have you ever done it? have you ever released a mod with content from a licensed game? because i have, and no such thing ever happened to me. maybe i was lucky, who knows, but i know for one thing they can't sue if you don't sell it, well, they can technically sue for anything but it would most likely end in a settlemtn to just stop what you're doing, which a simple cease and desist will do. which is of course entirely possible, the point is, even if you don't release it, or if you get a cease and desist, you're making the mod for yourself. most of the mods i do for games, i don't even release, i just make a model, use it in the game because i like it, and be done with it, bigger more complex mods i use for multiplayer with freinds and other stuff, so honestly, who the hell cares what the legal consequences are. they're not that bad, that is IF you even release it. the part we're dealing with here is the actual construction of the mod, that part doesn't hurt the creators of the original product, so why are you wasting your time telling these folks how much of a criminal they will be? i know, probably the same reason i'm wasting my time explaining this to you, to be annoying, right?
(i've delt with people with your attitude before, it's highly annoying, i assure you)