Smarty Template Structure
The templates of the frontend resides in the frontend/templates/[project name] directory. There should be one main template (e.g. index.tpl) including the basic layout (menus, toolbars, css inclusion, etc.) which at some part include the content template which fits the current page. In smarty, this happens by setting a {include file=$coretpl} tag.
Therefore, you will have to define the $coretpl variable for each page in the according case inside the event handler.
For more information about smarty, please visit http://smarty.php.net/manual