change user name?

Hi.
I have seen some solutions in ASP. http://msmvps.com/blogs/omar/archive/2006/08/18/how-to-change-user-name-in-asp-net-2-0-membership-provider.aspx
Now this may work  inside .net code but you must create a new user and migrate. I was thinking of a solution in SQL and i've read that you can rename the username and loweredusername in the users table.My concearn is that you can have another application using the same username inside the same database.So i think it is possible to also change a user with the same name from another application by accident.
I have seen that membership.provider.applicationame will give you the app name but in the sql database under the aspnet_Applications i have seen my application name and also a row with "/" as the Applicationname.
I also have seen duplicate usernames in aspnet_users. So either i have done something wrong when i created the asp database or this is a default behavior.

Can someone en ...