I\'m using FormsAuthentication for an ASP.NET site that has a master page that displays the current logged in user, Page.User.Identity.Name.
They can change their us
Though MasterMax's suggestion is what I would do, you can actually update the Page.User via HttpContext.Current.User.
If you know the user's roles (or you aren't using role based authorization), you can take advantage of the System.Security.Principal.GenericPrincipal class:
string newUsername = "New Username";
string[] roles = new string[] {"Role1", "Role2"};
HttpContext.Current.User =
new GenericPrincipal(new GenericIdentity(newUserName), roles);