Surely the nightmare for you would be if lads from the South were suddenly eligible for NI (or some other country)? We'd take Shay Given, who's a "Northerner" as it is...;)
As for the involvement of the Dept. of Foreign Affairs (aside from the irony that you don't mean the Dept. of Irish Affairs!), as I keep saying, FIFA do not deal with Governments, they deal with their own Member Associations on matters such as these.
Still, I know from some of your previous posts that you have absolute confidence in the competence of the FAI when dealing with such matters...:D