It is another thing entirely to piggy-back on an existing product without expecting the original product's developer to demand some sort of compensation.
I would love it if I could see the Olympics coverage with the annoying voices of the politically correct announcers replaced by witty and snarky commentary by someone such as Trey Parker and Matt Stone of South Park fame.
Unfortunately that's not gonna happen.
Adding some mod to Grand Theft Auto that requires a user to violate the purchase agreement in order to activate the mod is something that might be great in theory, but doesn't work in a free market system backed up by legal contracts enforced by a justice system.
The creators of Quake (id software) published the technical specifications for their game and encouraged people to produce new levels or mods for it. Since playing those levels or mods required buying the original game, the existence of hundreds of high-quality levels and mods (by now, thousands I'm sure) someone who spent $40 for Quake wouldn't just get to play 30 levels from id, but hundreds of other levels as well. A real bargain.
Adding some mod to Grand Theft Auto that requires a user to violate the purchase agreement in order to activate the mod is something that might be great in theory, but doesn't work in a free market system backed up by legal contracts enforced by a justice system.
If I purchase a piece of software, and have not agreed to any license prior to the seller's acceptance of my payment, I am not bound by any purchase agreement.