[Analogpoint]

If there's a template hook available where you want to add some output, just add what you want to it:

$template_hook['some_template_hook'] .= $parsed_template_or_html_output;

You can also use str_replace or preg_replace to search for code within a template and add something before or after it.

For example
$vbulletin->templatecache['navbar'] is the navbar template.

If you give a concrete example of what you want to do, I can be of more help.