If i change my username to new one, What happen to my old username, Can anyone register with my old username ?!
No. And the page with the old username will be redirected to the new one.
Looks like it will not work. Here is more info. See the last notice: http://support.envato.com/index.php?/Knowledgebase/Article/View/229/50/how-do-i-change-my-username