Rename Completed Order Status to Shipped

add_filter( 'wc_order_statuses', 'wwccs_rename_completed_order_status' );
 
function wwccs_rename_completed_order_status( $statuses ) {
   $statuses['wc-completed'] = 'Shipped';
   return $statuses;
}
 
add_filter( 'woocommerce_register_shop_order_post_statuses', 'wwccs_rename_completed_order_status_counter' );
  
function wwccs_rename_completed_order_status_counter( $statuses ) {
   $statuses['wc-completed']['label_count'] = _n_noop( 'Shipped <span class="count">(%s)</span>', 'Shipped <span class="count">(%s)</span>', 'woocommerce' );
   return $statuses;
}