This is a bit strange, as I am aware of several people who have changed their user name several times- and yet Forum Netiquette clealy says this is not allowed:
Username-changing
We don’t allow members to change their usernames because we want everyone to be able to trust the relationships they build up with others on Gransnet.
Not sure what the problem is, but I would never change my user name- even though there are some posters who 'jump on my back' on a very regular basis. It wouldn't work anyhow, as style, syntax and personality, etc, would soon be picked up. I've picked this up with posters who have changed their name in the past- it was very soon clear who they were.
Just ask the person who is sending you unwanted messages with links to stop. Much better. Bonne chance.