title: assign a new value to a $_GET variable
body: <p>We always retrieve the value in a <code>$_GET['var']</code>, but is it possible to assign a value as well? I have a php page where at one point, through ajax, I want to stay on the same page but change the query string or do an assignment like this:</p>
  
  <p><code>$_GET['myvar'] = 'newvalue';</code></p>
  
  <p>Is this possible?</p>