title: Change the value of a previously-defined constant
body: <p>I have defined a constant in PHP e.g.</p>
  
  <pre><code>define('CONSTANT_NAME', 'constant_value');
  </code></pre>
  
  <p>I want to be able to change the value of this constant later on in the code.</p>
  
  <p>Can this be done? If so, how?</p>