title: Filter HTML Content of Plugin
body: <p>I am using the Marketpress plugin. I want to modify <code>single_order_funct()</code> function HTML content in it. I want to make changes so that, when it is updated, I don't lose them.  </p>
  
  <pre><code>&lt;?php
   class PluginClass{
     function single_order_funct() {
  ?&gt;
      &lt;h1&gt;test&lt;/h1&gt;
  &lt;?php
    }
  
    function orders_funct() {
      if (isset($_GET['order_id'])) {
        $this-&gt;single_order_funct();
        return;
       }
    }
  </code></pre>
  
  <p>Whenever <code>single_order_funct()</code> function is called, I want to modify the HTML content it returns. How can I do it with <code>remove_action()</code> and <code>add_action()</code> or is there any other way to do it?</p>