Copyright protection includes "Derivative works". That's why I can't write a "Star Wars" novel and publish it. Copyright protection does not apply to mods, heads, etc. You can quote ad infinitum about the rights granted under copyright protection, but it's a waste of space here,
it doesn't apply. You can only copyright creative works.
From wikipedia:
A
creative work is a manifestation of
creative effort such as
artwork,
literature,
music, and
paintings.
Creative works have in common a degree of arbitrariness, such that
it is improbable that two people would independently create the same work.
If copyright would apply, I would copyright human DNA, and charge a royalty from every living person on the planet, since they are all "derivative works". Or copyright my own DNA and claim that every other human being on the planet is using my copyrighted material without authorization.