title: How to "append" Op at the beginning of a TensorFlow graph?
body: <p>I have a <code>GraphDef</code> proto file which I am importing using <code>tf.import_graph_def</code>. Ops can be added at the end of the graph like this:</p>
  
  <pre><code>final_tensor = tf.import_graph_def(graph_def, name='', return_elements=['final_tensor'])
  new_tensor = some_op(final_tensor)
  </code></pre>
  
  <p>But I want to add Ops at the beginning of the graph, so essentially the first Op in the graph_def needs to take the output of my Op as input, how do I do it?</p>