Nope, you have to create a new account. Sony planned poorly in that respect.
+1 to the *Sigh* I've sent many email to Sony hoping they add the ability to change the country. It would make our gaming lifes much easier.... Well here is the thread I made, Please support it and put all your information in this one thread so we can get Sony's attention: http://boardsus.playstation.com/playstation/board/
I tried to make it as neat as possible.