A player that is already a registered player of a National Chess Federation (NCF) is required to register separately with FIDE to obtain a FIN?
According to http://www.fide.com/fide/handbook.html?id=180&view=article I'd say no
All NCFs are required to register their players with FIDE. The FIDE Regulations on Registration, Transfers and Eligibility shall apply. All players who already have a FIDE ID number before 1 January 2015 are considered to be registered.
But I've been asked by a Fide arbiter to tell the player the procedure (and that he has to pay 25€ for that).
The player I'm talking about has been registered already in the NCF for 2016 and 2017.