I don't think self-reporting is the answer.
You MIGHT be able to determine location based on a traceroute, though anycast would surely derail such attempts. I suspect most people rely on 3rd party GeoIP databases, and that those companies aren't interested in hearing from you about your location change, mostly because they are worried that if they do, the evildoers will overrun them with bad requests, or bait and switch, making their data less accurate than it is now without your block being correct.
Having recently leapt through a few GeoIP hoops to see about getting records fixed[1], perhaps the NANOG wiki could feature 'known ways to fix GeoIP' and be used as a reference? Seems to be something that's going to be more, not less, significant to customers and network operators alike going forward. Mark. [1] http://www.merit.edu/mail.archives/nanog/msg13895.html