The constitutional claim over the entire island was declaratory and aspirational in nature - not actually enforceable - and was restrained further from being achieved via anything other than peaceful, diplomatic means by other constitutional provisions upholding the binding nature of international law upon the actions of the Irish state. Besides, the Irish courts found, possibly on more than one occasion - I would need to confirm - that there was no legal obligation placed upon the state to actively seek the re-unification of the whole island.
I don't think anyone could ever have thought the claim over the whole island as the national territory might have manifested itself in aggressive military action or anything of the sort anyway. The notion of the Irish state militarily taking on the UK in a territorial conflict makes me chuckle more than anything; the idea of it ever being anywhere near a real prospect would have been preposterous, in spite of the rather romantic and optimistic street-rumours that circulated the Bogside of the Irish army marching in the Letterkenny Road the day Jack Lynch announced that he "could not stand by and watch innocent people injured and perhaps worse" during the events there in August of 1969 that came to be known as the Battle of the Bogside. This statement of "intent", which was interpreted by the outraged unionist community as an announcement of impending military invasion, amounted to little more than the Irish army setting up medical outposts for the injured residents of the Bogside along the Irish side of the border in Donegal.
Regardless, I do fully acknowledge how the former wording wouldn't have sat well with the unionist community in the north. I'd be going down a rather disingenuous route to attempt the argue that the claim wasn't an irredentist one under international law prior to 1999. That's something of which I can't deny the legal reality no matter what my own personal political stance might be regarding the aspirations of the my country with relation to Northern Ireland. The amendment of both worded intent and actions are, of course, a significant aspect of winning over hearts and minds in any conflict resolution.
Anyway, as you point out, the territorial claim has long been removed, but I still frequently encounter accusations that the extra-territorial applicability of Irish citizenship amounts to some sort of hostile irredentism. There are connotations in that that it might be illegitimate or legally questionable. Unfortunately, it's been expressly described as such by some of the more vocal and articulate posters on this issue on OWC, who one might have hoped would have been able to maintain a more level head, especially since its extraterritorial applicability was democratically vindicated (I think that's a fair enough description to use) in the north and further acknowledged by the UK government. In fact, you above, have just described it as an "anomaly" used to "exploit" FIFA's statutes, as if to de-legitimise it altogether. The laws regarding Irish citizenship, which have existed long before FIFA drew up its latest set of statutes, were not worded with the idea of exploiting or "subverting" the statutes of any external sports governing body in mind, as seems to be your implication, especially with your raising of the Qatari passport issue. The statutes that this body - FIFA - have composed themselves happen to permit the citizenship laws' application in the footballing sphere, which is perfectly natural, and maybe even something that FIFA took into account when wording their current statutes, seeing as they have always indicated through both words and action that they support the FAI's outlook on matters relating to this issue. A seemingly unique situation as regards the applicability of citizenship, yes, but to describe it as an anomaly would nearly suggest FIFA had made an error in overlooking something when formulating their rules. That patently isn't the case at all.