I've registered custom rewrite rules and `query_vars` to use for displaying a list of events based on ISO date format. For example when a user requests the URL, `http://site.com/by-date/2013-04-04/`, my `query_var` is the date portion and I'd like to display a list of events who's `meta_key` of `_event_scheduled_date` equals the ISO date value in the `query_var`.

Whenever I try the following code to modify the `$query` in `pre_get_posts` WordPress initiates a 404 and no posts are queried. I've been able to use `pre_get_posts` to manipulate other taxonomy listings and archive pages, but have yet been able to get it to work correctly with the custom `query_var` I've created.

    function rewrite_rule_by_date() {
    	add_rewrite_rule('(by\-date)/([0-9]{4}\-[0-9]{2}\-[0-9]{2})$', 'index.php?pagename=$matches[1]&event_date=$matches[2]', 'top');
    }
    add_action( 'init', 'rewrite_rule_by_date' );
    
    function query_var_by_date() {
    	add_rewrite_tag( '%event_date%', '([0-9]{4}-[0-9]{2}-[0-9]{2})');
    }
    add_action( 'init', 'query_var_by_date' );
    
    function custom_event_query( $query ) {
    	if (  is_page( 'by-date' ) && get_query_var( 'event_date' ) && is_main_query() ) {
    		$query->set( 'post_type', 'event' );
    		$query->set( 'post_status', 'publish' );
    		$query->set( 'meta_key', '_event_scheduled_date' );
    		$query->set( 'orderby', 'meta_value' );
    		$query->set( 'order', 'ASC' );
    		$query->set( 'post_per_page', -1 );
    		
    		$meta_query = array(
    			array(
    				'key' => '_event_scheduled_date',
    				'value' => get_query_var( 'event_date' ),
    				'type' => 'DATE',
    				'compare' => '='
    			)
    		);
    
    		$query->set( 'meta_query', $meta_query );
    	}
    
    	return $query;
    }
    add_filter( 'pre_get_posts', 'custom_event_query' );