add_action( 'woocommerce_new_order', 'pending_new_order_notification', 20, 1 );
function pending_new_order_notification( $order_id ) {
// Get an instance of the WC_Order object
$order = wc_get_order( $order_id );
// Only for "pending" order status
if( ! $order->has_status( 'pending' ) ) return;
// Get an instance of the WC_Email_New_Order object
$wc_email = WC()->mailer()->get_emails()['WC_Email_New_Order'];
## -- Customizing Heading, subject (and optionally add recipients) -- ##
// Change Subject
$wc_email->settings['subject'] = __('{site_title} - Pending order ({order_number}) - {order_date}');
// Change Heading
$wc_email->settings['heading'] = __('Pending Order');
// $wc_email->settings['recipient'] .= ',name@email.com'; // Add email recipients (coma separated)
// Send "New Email" notification (to admin)
$wc_email->trigger( $order_id );
}
codesandbox