change-idoklad-invoice-description.php

<?php
$description = 'Proforma za objednávku č: '.$order_id;
$data['Description'] = apply_filters( 'idoklad_proforma_description', $description, $order_id );
add_filter( 'idoklad_proforma_description', 'toret_change_idoklad_proforma_description', 10, 2 );
function toret_change_idoklad_proforma_description( $description, $order_id ){
  return 'Zálohovka';
}

$description = 'Faktura za objednávku č: '.$order_id;
$data['Description'] = apply_filters( 'idoklad_invoice_description', $description, $order_id );

add_filter( 'idoklad_invoice_description', 'toret_change_idoklad_invoice_description', 10, 2 );
function toret_change_idoklad_invoice_description( $description, $order_id ){
  return 'Mega faktura za objednávku!';
}