The full range of everything we do is available to anyone who asks. You have to email hn@ycombinator.com, as the FAQ explains (https://news.ycombinator.com/newsfaq.html), but there's no restriction on whom we help, or how. We help people who have abused this site for years and then ask us (sometimes exceedingly impolitely!) to clean up what they did, and we treat them the same way as we treat anyone; I may grit my teeth while doing it, but that's all. Why? Because it's best for the community in the long run if we treat everyone the same way, and because—as I tell users who email—we don't want anyone to get in trouble from anything they posted to HN.

Even more than that, one of the administrators previously told me via email that HN is not able to rename accounts (presumably they use account names instead of numeric IDs as a key somewhere). So the only explanation for the displayed author on that post having changed is that they switched the author of the post, the original author's account could not have been renamed.