Individually you cant change your username but you can make a request to Theymos for change of username. Once he approved it, in a few days it will be changed. There is a reason why it is meant to be that way.

Although 7 to 8 years ago you will need to become a VIP member first by donating 50 BTC but that is different now. You dont have to donate anything, you just need to have good contribution to the forum.