On the side of showing when the user changes their username, they made a statement that is against that; if someone for any reason changes their name, there is no need to make it too obvious that they did change it; it could be a security risk to their privacy.
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.
Now donation is no longer needed and accepted to the forum, but the change of username request I believe is open to anyone; you just have to make your result with good reason, and it's left for the admins to decide if your request is worthy enough.