RME views: Vehicles were on the road before UN R155 came into force. Retrofitting extends vehicle life in line with climate action and circular economy objectives. Retrofitters must be responsible only for components involved in the transformation and any parts they add or modify, not for original vehicle components. A risk management demonstration dossier limited to the transformed system must be included in transformation approval applications. If the origin vehicle is not R155-approved, retrofitters may provide the dossier without laboratory tests. If R155-approved, authorities decide on compliance, requiring laboratory tests if needed. Manufacturers’ data are not accessible to retrofitters. The application of cyber security provisions (i.e., UN R155 compliance) should be delayed by two years from the entry-into-force of the new regulation for the approval of EC/HFCV retrofit systems and revisions to UN R155 should also provide two-year transitional provisions before the application to the retrofit regulation.