I'm pretty sure "no" unless you had good enough of a reason (and reputation) to warrant pg actually changing it for you in the database. I'm not sure he's ever done this.
Your rep is similar to mine, though, and I consider myself still in "newbie" ranges -- I mostly lurk, and have only had a handful of popular comments along the way. So just grab a new username and start from scratch.
Karma doesn't buy all that much for you, anyway, on HN.