title: woocommerce change customer subject line
body: <p>I want to change the woocommerce_email_subject_customer_invoice but this one just edits the admin new customer order subject line. can you show me how to edit this correctly to be able to change the email subject line that the client uses. </p>
  
  <pre><code>       /*
          * Subject filters: 
          *   woocommerce_email_subject_new_order
          *   woocommerce_email_subject_customer_procesing_order
          *   woocommerce_email_subject_customer_completed_order
          *   woocommerce_email_subject_customer_invoice
          *   woocommerce_email_subject_customer_note
          *   woocommerce_email_subject_low_stock
          *   woocommerce_email_subject_no_stock
          *   woocommerce_email_subject_backorder
          *   woocommerce_email_subject_customer_new_account
          *   woocommerce_email_subject_customer_invoice_paid
           **/
          add_filter('woocommerce_email_subject_new_order', 'change_admin_email_subject', 1, 2);
  
          function change_admin_email_subject( $subject, $order ) {
         global $woocommerce;
  
         $blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);
  
          $subject = sprintf( '[%s] New Customer Order (# %s) from Name %s %s', $blogname, 
          $order-&gt;id, $order-&gt;billing_first_name, $order-&gt;billing_last_name );
  
          return $subject;
          }
  </code></pre>