Modify main loop in taxonomy archive page

Is there a way that I can modify the main loop in a single taxonomy template, but leave it untouched in every other template?

In this case, I have a custom post type called “Events” which in turn has a custom taxonomy called “Region”. What I want to do is, instead of listing each custom “Events” post chronologically by post date I want to order it by a custom meta value (In this case event_date).

I only want to do this in my taxonomy-region.php template and leave any other instance of the main loop untouched.

You could hijack the $query just before fetching the posts.

function wpdev_156674_pre_get_posts( $query ) {

    if (
        $query->is_main_query()
        && $query->is_tax( 'region' )
    ) {
        // Manipulate $query here, for instance like so
        $query->set( 'orderby', 'meta_value_num' );
        $query->set( 'meta_key', 'event_date' );
        $query->set( 'order', 'DESC' );
    }
}
add_action( 'pre_get_posts', 'wpdev_156674_pre_get_posts' );

References:

• pre_get_posts action hook
• WP_Query class