title: How to change Enum possible values
body: <p>The following code does not work:</p>
  
  <pre><code>from traits.api import HasTraits,  Enum
  
  class A(HasTraits):
  
      enum = Enum(1,2,3)
  
  class B(A):
  
      def __init__(self):
          self.trait('enum').default_value = ['one','two','three']
  
  b = B()
  b.configure_traits()
  </code></pre>
  
  <p>Instead of having the choice ['one','two','three'] in the drop-down list, it is still [1,2,3]. Is there a way to modify an Enum content in any way after it has been declared once?</p>