often they don't know which characters are going to be CoC when they're writing the scripts because they don't specify what race they want to be cast in that role.

I'm not convinced that's much of an excuse. First of all, Henriksen was around for a year. Surely at some point before "Jus in Bello" got written, somebody must've noticed that they'd cast a black man. Second of all, doing story revisions to account for unforeseen factors is an ordinary part of a TV writer's job description. They do it if a location becomes unavailable, or an actor sprains an ankle, or the FX budget runs out or filming gets delayed due to weather. I don't think it's inconceivable that they could say, "hey, we've cast a minority actor here, let's go over the script to make sure we're not portraying the character offensively."