title: NLTK: can I add terminal to grammar that is already generated
body: <p>I have generated grammar from atis grammar, now I wanted to add some rules of my own especially terminals from sentence could I do that?</p>
  
  <pre><code>import nltk
  grammar = nltk.data.load('grammars/large_grammars/atis.cfg')
  </code></pre>
  
  <p>to <code>grammar</code> I want to add more terminals.</p>