Roddenberry wrote the lyrics so that he could get half the royalties from the sheet music sales. They were never intended for any other purpose.
To clarify, Roddenberry didn't just collect royalties from the sale of the theme music's sheet music -- he collected fifty percent of all
the royalties related to the Star Trek
theme music, including performance royalties.
Reading further, David Alexander's biography states that Roddenberry finished the lyrics in December of 1965 (Star Trek Creator
, 1994, p.235). This lines up with Inside Star Trek: The Real Story
, which states that Courage was contacted about the 50-50 royalty split "after NBC put Star Trek
on its schedule" (p.185).
In my mind, this casts further doubt over the claim that Courage departed the series over the royalty dispute with Roddenberry. NBC picked up the series in February of 1966; Courage didn't record his scores for 'The Man Trap' and 'The Naked Time' until August of 1966, a full six months later.