It's extremely rare that we'd edit a comment but I don't think you have property rights over this one, so I'm going to redact the username you put in there and ask you not to do this again.
HN threads are collaborations; comments aren't just individual property. Active threads develop quickly in response to existing posts, and editing/deleting earlier comments removes context that the later ones are based on. The longer the time window, the more likely that later comments will get invalidated and/or history rewritten. So we need an edit window that's long enough for people to refine their comment or have second thoughts about it, but brief enough not to pull the rug out from others.
We're happy to delete comments or sometimes even edit them after the fact if people have a good reason for needing that (e.g. they're worried about getting in trouble from something they posted). But we only do that in response to specific requests about specific links. We don't delete history wholesale.