It would be nice to be able to at least retroactively anonymize your username. When we were living in a kinder world, I didn't think twice about using my real name as my username, but I echo GP's fear: Norms change through time, and I guarantee that something I posted years ago that was benign and uncontroversial then would get me fired today.

EDIT: Reading the other responses, it looks like HN will actually do this if you ask. Nice to know! +1 to the request to automate this and provide UI for it for users to self-serve.