"Grandfathering", a process applied in other aviation sectors, cannot be applied to aerodromes, as there is no single set of harmonised requirements against which aerodromes have been licensed/certificated. Indeed, in some Member States aerodromes have not been certificated at all. It is therefore necessary to carry out a "conversion" process on all aerodromes within scope. EASA has indicated that all aerodromes with existing licences will be eligible for an initial certificate under the EASA system (if they fall into the EASA scope). There will be a conversion process, which involves building a Certification Basis that takes into account existing exemptions and variations by the use of three options, the options being an Equivalent Level of Safety, Special Condition or the Deviation Acceptance and Action Document (DAAD).
Further information on the conversion process can be found on the EASA website - then select 'Aerodrome. Conversion and DAAD FAQs'.