I'd just like to say that I had no idea who "Tony Cascarino" was until I looked him up after reading this thread.
And I laughed out loud. Poor guy. I kept picturing this as a Blood Bowl special play card. "Eligibility Scandal!!". So thank you for that
Anyway, I've let people know in my New England league. I don't expect to find anyone who'll fly over but you never know.
(And if someone does bite, it'll be an American who swore he's totally a quarter Irish that one time he was hitting on a redhead at a St. Patrick's day party.
They will likely also confirm every stereotype about Americans which exist in Ireland. Yeah, we stole your holiday. sorry about that.

)
Anyway ... if there is a united Ireland team at Eurobowl 2018, I can not imagine players on that team being banned from a future Republic of Ireland or Northern Ireland team. The goal of the Eurobowl committee is to run a tournament, they have a basic amount of common sense and will certainly do what they need to support new teams.
Also, although it's none of my business, I like the idea of a unified team, because there's a larger chance of getting 8 players together, and because it makes me feel all warm and fuzzy when people get along peaceably (to play violent sports games)

Just maybe discuss beforehand what happens if you win hosting rights!