code: def modify_model_backprop(model, backprop_modifier):
      """Creates a copy of model by modifying all activations to use a custom op to modify the backprop behavior.
  
      Args:
          model:  The `keras.models.Model` instance.
          backprop_modifier: One of `{'guided', 'rectified'}`
  
      Returns:
          A copy of model with modified activations for backwards pass.
      """
      raise NotImplementedError("Theano version is not supported yet.")
  
label_desc: Use image node_id 1 for calling a global function with example usage: modify_model_backprop(model, backprop_modifier) without return types