No, it is not required.

Aeromedical assessments shall be carried out by any professional authorised by an EASA authority for that purpose.

Regulation (EU) 1178/2011: MED.C.005(c).

If your flight attendant certificate is no longer valid (unless the certificate has been suspended or revoked) you will have to re-take the initial training at an approved centre or air operator, take the associated examination and re-apply.

The issue may in this case be made in any EASA member country.

Regulation (EU)1178/2011: CC.CCA.100.

No; you can only hold a valid Flight Attendant Certificate issued by a single EASA aviation authority.

The cabin crew certificate issued by any EASA authority is recognised in all Member States and it is not necessary or possible to change certificate, issue a new one in another authority or transfer it between authorities to work for an operator in another Member State than the issuing Member State.

Cabin crew member certificates are issued for an unlimited duration and shall remain valid unless:

(a) suspended or revoked by the competent authority; or

(b) the holder has not exercised as a flight attendant during the preceding 60 months on at least one aircraft type; or

(c) the holder has completed the initial training more than 60 months ago without having exercised, after the issue of the certificate, as a flight attendant.

The certificate holder shall keep the necessary documents to be able to prove that the certificate is still valid.

Cabin crew attestations are issued for an unlimited period and shall remain valid unless: 

a) are suspended or revoked by the competent authority; or

b) the holder has not exercised as a TCP during the preceding 60 months on at least one aircraft type; or

c) the holder completed the initial training more than 60 months ago without having exercised, after the certificate was issued, as a TCP. 

The certificate holder shall keep the documents necessary to be able to prove that the certificate is still valid. 

The operator shall retain, and make available on request, the cabin crew certificate, roster, training and checking records pertaining to his type or variant of aircraft qualifications, unless such records are maintained by the operator employing his services and can be made available promptly on request to a competent authority or to the operator.

Regulation (EU) 1178/2011: CC.GEN.025(b).