mysql_change_user()
int mysql_change_user(user,password[, database, connection])
This function can be used to change the username for a MySQL
connection. The new username is given as the first argument and the
password for that user as the second. A different database from the
one in use may be given as a third argument. You can change the user
information for a different MySQL connection by specifying it as the
fourth argument. If the function is successful, it returns true; if
it’s unsuccessful, it returns false. This function is no longer
available as of version 4 of PHP. Instead, you should establish a new
connection with a different user by using the
mysql_connect() function.