But that's not what happened regarding Lorca. They didn't wrote a badish character and then suddenly chickened out and come up with the idea, that he could be from the Mirror Universe to explain his shitty behavior.
The character was conceived as from the Mirror Universe from the beginning, but it always was planned as a twist for the audience. And for a twist, the audience has to believe in the pretended truth, that the twist will destroy. That's why they went all-in on trying to sell the idea that Lorca was intended to be a protagonist. They even sent their showrunners into interviews with populist bullshit arguments why Lorca was good. Bullshit sentences like "he gets things done!", "he is a patriot!", "If you don't like him, you hate America!"* and similar phrases which are used when you have zero argument for something, but still want people to believe you. (* the third one they didn't say - as far as I know).
What really buffled me was how many people in an absolutely naive way fell for it and said that Lorca is a good person, although the series' first episodes clearly show that he totally isn't. The reveal that he was from the Mirror Universe did not make him one-dimensional. He was it all the time, only the reveal explained why.
The one thing they really changed only later on is Security Chief Landry. She was supposed to be from the Mirror Universe (thrown to our universe together with Lorca) - which explains her totally irrational, dumb, aggressive behavior that finally qualified her for a Darwin Award. But reportedly, the actress was such a delight to work with, that they scrapped the idea that she was from the Mirror Universe, so that they could bring her back to play her counterpart in the Mirror Universe episodes.