add_action and set_role

In my user registration, the user can them selves choose their role.
But I have not been able to hook this up with user registration.

I’m also not able to run my function from my plugin using add_action.

So what I do now, is to call my function on page load (Above the header – before <!DOCTYPE>).

Unfortunately the user have to reload the page to see the effect. I’m currently looking into how I can solve this problem, and change user role before anything else is loaded (that is role based).

Here is my function:

function changeUserRole()
{
  global $current_user;
  get_currentuserinfo();

  $user_ID = $current_user->ID;
  $user = new WP_User( $user_ID );
  $roles = array(... list of roles...);

  // Set new user role.
  foreach($roles as $role => $name) {
    if( $current_user->role == $name)
      $user->set_role($role);
  }
}