According to the Registered Exporter (REX) Guidance Document only companies established in the EU are allowed to become registered exporters. Please find below an extract from the Guidance Document (https://ec.europa.eu/taxation_customs/sites/taxation/files/registered_exporter_system_rex_-_guidance_document_v1_en.pdf).
In most EU countries it is not possible for non-established entity to act as exporter in box 2 of the SAD document (i.e. customs declaration). It seems however that e.g. Portugal and Poland is still allowing non-established entities to act as exporters. However, this is contradicting to the European customs legislation (please see UCC DA article 1 (19). Therefore, even for Portugal/Poland the setup for exports should follow the general concept with the local entity (company established within EU) acting as exporter and the non-established entity being mentioned in box 44 of the SAD document.
Conditions for becoming registered exporter
Any exporter established in the territory of the European Union, is entitled to apply to the competent customs authorities to become registered exporter, provided that the company holds, at any time, appropriate evidence of the preferential origin of the products he intends to export, for the purpose of checks carried out by the customs authorities.
An EU company which has its headquarter in a Member State and premises or warehouses in another Member State may request its registration in any (or both if the different companies have different EORI numbers) of these Member States. A company which is already registered in a Member State with its EORI number cannot request to be registered in another Member State with the same EORI number.
For any further information please contact Paavo Östberg, firstname.lastname@example.org.