Yes, I believe you can since the member named Lugia does it all the times, if you want to know how, try to ask him since I have no idea how to, but he does.
Edit: Just asked him, he said that you should just look if that username is available and when you find out it is contact forum administration and ask them to change your name nicely
Edit: Just asked him, he said that you should just look if that username is available and when you find out it is contact forum administration and ask them to change your name nicely
Click them or they will click you