I recall that it in that era there were cases if you wrote an episode of a show you held a production position on like producer, then you didn't own any rights to things you created in one of your scripts. Thus, because Gene L. Coon was producer of Star Trek when he wrote the episode that introduced the Klingons, he held no "creator" claim on that concept. OTOH, Harlan Ellison as a writer for hire was known to throw fits if any of his elements were reused in another script without his being asked. It's sort of a gray zone I guess, but the producers I think in this case had to think that if they covered their bases by changing the name, then Black at least would have known he wouldn't have a case if he tried to object.

Lending further credence to this is the fact that Black also wrote "The Box" in which Big Chicken returns, so there wasn't a similar issue with that episode. OTOH, the fact that Black was not the writer of "Six Kilos" may explain why Gerald S. O'Laughlin's "Carl Swanson" from that episode is suddenly "Charlie Swanson" (and why the episodes were reversed in airdate order even though from a logical consistency standpoint, the Swanson character should be one and the same. But because of these tricks, then you can make a technical argument the two episodes are not connected in the same way "The Box" connects to "And They Painted Daisies On His Coffin" with Big Chicken).