///////////////////////////// class Mage_Adminhtml_Block_Customer_Edit_Renderer_Newpass //////////////////////////////////////
public function render(Varien_Data_Form_Element_Abstract $element)
    {
        $html  = 'stuff';
        $html .= 'more stuff';

        return $html;
    }

////////////////////////////// Module File Below //////////////////////////////////////////
class John_MyModule_Block_Adminhtml_Customer_Edit_Renderer_Newpass extends Mage_Adminhtml_Block_Customer_Edit_Renderer_Newpass
{
    public function render(Varien_Data_Form_Element_Abstract $element)
        {
            parent::render($element);
            // I want to append some html here
            return $element;
        }