You are right in thinking that we should not editorialise when we post a link to HN but sometimes (just sometimes) the original title just fails to reflect the nature of the item and is downright discouraging to any potential browser.
OK - we are all enjoined to post only that which is worthy and interesting to our fellows but with the volume of posts increasing there is a subtle divergence in (not quality - but content subjects perhaps) that occasionally needs a small title change to ensure that the subject is clarified.
Agreed, and also it's worth mentioning that the author of the article isn't the person who chooses the title unless it's a blog post. The title the editor picks is chosen to fill up the amount of empty space available, usually after reading only the first couple paragraphs. If the title doesn't reflect what makes the story interesting or compelling, then by all means change it. This is especially true for sources like Wired that like to pick some cutesy title that has nothing to do with the article; in these cases just grab the bold text or the topic sentence and use that as either a title or subtitle.
The problem with the original poster's suggestion is that the original headline was written to be seen in context. Usually this means that it is accompanied bny full text that can be seen at a glance, sometimes it means that it is seen with a brief summary.
HN is splendid, but as a noob, I find myself grinding my teeth that I have to click on every single damn link to see what the story is actually about. I mean "Tim O'Reilly to software developers: get serious" what's that actually about? Anything worth my time? who knows.
OK - we are all enjoined to post only that which is worthy and interesting to our fellows but with the volume of posts increasing there is a subtle divergence in (not quality - but content subjects perhaps) that occasionally needs a small title change to ensure that the subject is clarified.