<!DOCTYPE HTML>
<html>
<head>
  <script>
    function tweak() {
      var olderShadow = document.getElementById('outer').createShadowRoot();
      olderShadow.innerHTML = '<div style="width:100px; height:100px; background-color: orange"><content></content></div>';

      var youngerShadow = document.getElementById('outer').createShadowRoot();
      youngerShadow.innerHTML = '<div style="width:100px; height:100px; background-color: green"></div><shadow>Hello World</shadow>';
    }
  </script>
</head>
<body onload="tweak()">
<div id="outer">
  <div style="width:300px; height:100px; background-color:red;"></div>
</div>
</body>
</html>