You cannot extend the current control, because there are many methods that cannot be overridden and this control is wrapped in another control - ManageUsers which also has its own events and logic which cannot be easily replicated. The easiest way would be to create a new control and hide the default one.
You can use ASP.NET GridView or RadGrid control and methods of MembershipUser, Membership, MembershipUserCollection, ProfileBase classes.
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