Modify the main query based on tag

gistfile1.php

//* Modify the main query based on tag
add_action( 'pre_get_posts','custom_tax_query' );
function custom_tax_query( $query ) {
	if ( $query->is_main_query() && $query->is_tag( 'west-valley-2015' ) ) {
		$query->set( 'posts_per_page', '3' );
		$query->set( 'order', 'ASC' );
		$query->set( 'orderby', 'title' );
	}
}