I can hold more than one Flight Attendant Certificate, issued by more than one EASA Aviation Authority.

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.

In this respect, the holder of a Flight Attendant Certificate must inform the operator for whom he/she is to serve as a cabin crew member of his/her possession of the certificate.

Holding more than one valid Flight Attendant Certificate may result in penalties for the holder.

Regulation (EU) 1178/2011: AMC1 ARA.GEN.315(a)