If I want to change some values on a template I will create my own template like this:
<div id='expert-cases'>
<div class='crm-summary-row expert-cases'>
<div class='crm-label'>{ts}Main Activities{/ts}</div>
<div class='crm-content'>{$countExpertCases}</div>
</div>
</div>
{literal}
<script type='text/javascript'>
cj("#tagLink").parent().parent().prepend(cj("#expert-cases").html());
</script>
{/literal}
in this example I add a field to the template and use jQuery to move it to the right spot. Yours is even simpler, you need to change the class. Adding the template to the form is then
CRM_Core_Region::instance('page-body')->add(array(
'template' => 'CRM/Threepeas/Page/ExpertCases.tpl'));
in the right spot. In you case probably in the buildForm hook of the Contribution page.