European Union Agency for Railways has confirmed that rolling stock in use before the entry into force of the 4th Railway Package, based on the RIV (Regolamento Internazionale Veicoli) or RIC (Regolamento Internazionale Carrozze) agreements, will still be authorised for use based on these agreements and in areas of operation where they are in fact in use.
In case of any modifications to such stock and qualification of such modification as requiring new authorisation for use (in accordance with Art. 15 of the Commission Implementing Regulation (EU) 2018/545 of 4 April 2018) the area of use determined in the new authorisation will remain the same, but only with regard to the area where the stock has actually been in use. The applicant, while filing an application for the new authorisation, is to prove the actual area of operation of the given rolling stock. Such proof may include data from the national vehicle register (NVR), maintenance documentation or an agreement with an ECM to perform maintenance activities in the actual area of operation, the confirmation of route allocation by infrastructure manager, agreements with railway undertakings on the services or introduction of such rolling stock on routes, but also a declaration of a railway carrier with regard to the actual area of operation of the stock in question.
You will find the full text of the Agency's recommendation under this link.