Load different template file when condition met?

If I visit a page on my WordPress site, WP goes and determines what template file it should use based on the template hierarchy.

If I’m doing some logic checking in the hook init and say my conditions are met, how do I tell WordPress to load a template file of my choosing, not the one WordPress would normally dish up?

Can you perform the logic on the template_include filter? Else, you could set a global/constant and use that in template_include to serve up the appropriate template.

The template_include filter filers the path to the template file to be included. To avoid errors you should check if the template exists – locate_template does this for theme/child-theme files.

add_filter("template_include", "sc_redirect_properties_to_registration");
function sc_redirect_properties_to_registration( $template )
{
    if( is_user_logged_in() && ! is_page("the-properties") )
        return $template;

    //You could include templates from plugins
    //$template = plugin_dir_path(__FILE__).'templates/plugin-template.php';

    //Best to check the template exists. With **theme/child-theme** templates
    // you can do this with locate_template.
    return locate_template('template-registration.php');
}