Since STET indicates that you DISAGREE with a comment/edit, there should be a word that indicates when you AGREE with a comment/edit. Might I suggest you add the word, "Concur," to your Set Actions list in each comment? Current use of "Completed," which is the closest thing to providing a definitive, as well as clear, indication of intent, is vague at best. Completed what? Does that mean I want the designer to make/not make the change? Or is that about the possible end to a round of comments on an edit?
Clearly, using the most descriptive and literal word(s) in editing/review situations is the best way to avoid any misunderstandings. Right now, our reviewers are typing "Concur" in each comment box in which this is the correct response so there is no need for the designer to equivocate about meaning. A simple click to select "Concur" would un-muddy the water!