With this method (supported by all major browsers, including IE 4), you can take an arbitrary HTML string, and insert it anywhere in the document.
<script>
document.getElementById('heading1').insertAdjacentHTML('beforebegin', '<h3 style="text-align: center;"><strong>Adding Classes</strong></h3>');
document.getElementById('heading5').insertAdjacentHTML('beforebegin', '<h3 style="text-align: center;"><strong>Dropping Classes</strong></h3>');
document.getElementById('heading6').insertAdjacentHTML('beforebegin', '<h3 style="text-align: center;"><strong>FAQs and Hints</strong></h3>');
</script>