You will have to renew your home country class 1 in order to transfer licence state. For example, the UK CAA will ask you to sign a release of your medical records to the new state. This is all through the aeromedical department.
When I changed from the UK to another EASA state, the new state insisted that my class 1 was current for transfer.
To be crystal clear, you cannot have say a Polish EASA licence and a UK EASA medical. You can, however, with few provisos, renew a Polish class 1 with a UK EASA examiner. In my case, a UK AME conducted a medical exam, gave me a UK class 1 certificate and I sent it to the IAA who then gave me (for free) an Irish class 1. That's only one way of doing it, there are others.