Hmm...”Fire Shatner. And lose the guy with the funny ears.”
Gene Rodenberry gave a presentation at my college (1975) in which he talked about the development of the series, showed some out takes, etc. I don't know about "firing Shatner", but I do remember him saying that when NBC agreed to pick up the series, they told him to "lose the guy with the funny ears." They felt that Spock wasn't a very believable character. Rodenberry resisted, and of course the character stayed. Also, he first offered Star Trek to CBS, who was looking for a Sci-Fi series at the time. They turned him down in favor of "Lost In Space."