I'm not punctilious about it; I usually add "Edit:" if the information materially changes the meaning of the comment. (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...)

In the case of the GP I changed my wording to be softer and refer directly to the site guidelines. (Originally it said "Please don't take HN threads on political flamewar tangents. Nothing good's going to come of it, whichever way you lean.")