The parent comment asked specifically about negating the finality of each state, which I addressed. As for how to actually implement complement in a regex engin

The parent comment asked specifically about negating the finality of each state, which I addressed. As for how to actually implement complement in a regex engine, there are certainly some strategies like the one you mentioned that could be used (but the point of my comment was that just swapping final/non-final states is not a valid one).