Year-end transfer pricing adjustments and the customs value

Customs value and transfer pricing could be likened to Siamese twins - that's how closely linked they are. Let's discuss some practical questions related to the year-end transfer pricing adjustments: If the price is revised upwards, does the importer have to go to customs and pay additional duties? If the price is revised downwards, is the importer entitled to a refund of duties? If the goods are duty-free and there is no excise duty, but only import VAT (which is deductible in any case)?