title: Load different page but keep original URL
body: <p>I want to build a function where I load to 1 specific page whenever the last part of the URL (slug) only includes numbers, I have a hard time finding a solution to my problem.</p>
  <p>I currently have an add_rewrite_rule function that brings any all numeric url-slugs to 1 specific page, which is good, but it's only one part of the puzzle... The originally written URL should remain the same in the browser, it should not redirect but instead load another page while keeping the same URL in the browser.</p>
  <p>Current function:</p>
  <pre><code>add_action('init', function(){
      add_rewrite_rule( '([0-9]+)[/]?$', 'index.php?p=49', 'top' );
  });
  </code></pre>
  <p>But instead of a browser url like <strong>localhost/callerid/nummer/0</strong> changing to <strong>localhost/callerid/nummer/nummer</strong> it has to stay <strong>localhost/callerid/nummer/0</strong>, but load the page of <strong>localhost/callerid/nummer/nummer</strong> (index.php?p=49)</p>
  <p>Summary: I want load the page of index.php?p=49 whenever the URL contains an all numeric slug, but keep the URL in the browser the same.</p>