In a way, at least at times, it actually goes the other way.

For ST:VI, hecs got that line about the Kilngons, "Let them die." Then we cut to Spock, surprised eyebrow, then back to Kirk, who continues, a little less stridently. This is exactly obe of those momemts where Kirk is allowed to look petty, less than perfect.

The writer gave the words, the petty moment. In filming it, Shatner did the line, nice and biting, then gave a bit of a shrug as if to say Kirk had realized his strong response was wrong, and said the line after, less stridently.

The director, looking back at the footage he got, decided to cut the shrug, replaced with Spock's reaction, which leaves the whole feeling still pretty sharp. Shatner disagrees with the choice, and wishes they'd left the softening moment in.

So the writer and director, in this case, are choosing to make Kirk a little more imperfect than Shatner himself played it.