asp.net mvc 3 - mvc3 formauthentication username to int value -

I am using formauthentication and as a user. Identity.name I am using are they are email, how can I change it for I can use they are unique registration ID instead?

  FormsAuthenticationTicket Ticket = New Form AuthenticationTicket (1, Model Email, DateTime.Now, Cookie Execution, True, Model. Email);   
 Model. Email is an email that users have and its string parameter I want to insert  model.RegistrationID  instead.  
  
 
 
 You can not change its data type but you can not change the form of the string as  RegistrationId  In database  
  FormsAuthenticationTicket ticket = new FormsAuthenticationTicket (RegistrationId.ToString (), model.Email, DateTime.Now, cookieExpiration, true, model.Email);