Lauri
JAR Fcl 3.005 covers transitional arrangements. Part 4 of the transitional arrangements states that existing holders of pilots licences issued by a JAA member state under their national regulations may continue to exercise the privileges of the national licence held, even if they cannot meet the requirements of JAR-FCL Part 3 (Medical).
You can read the exact wording on the JAA web site link below.
JAR-FCL 3.005