You can't change yours unless you could convince the admin to change yours
or
You could make another account and start over
Yes you can, but you have to have "Donator" status, which requires donating 50 BTC.
Wrong. Donating 50 BTC will get you a 'VIP' position and 'Donator' position for 10 BTC.
That looks right. And AFAIK, you need to be a VIP in order to change your title yourself.
As I noticed the following on the "Donate" page of the forum:
If you donate 10 BTC, you can get a special "Donator" title and a green "who's online" color. If you donate 50 BTC, you get VIP status and the ability to create a custom title for yourself. Both Donators and VIPs also get access to an exclusive forum section.
https://bitcointalk.org/donate.html