This post might be better suited to an Ireland board - many folks on the Member Trees board may not have a World Subscription.
On my own tree, if I input "Ireland," it stays "Ireland." If I am searching in trees, I see "Ireland (Northern Ireland)."
As I understand it, ancestry's algorithm uses current names - so the location for my relatives who were in lower North America in 1750 defaults to USA.
For my numerous Irish ancestors, I try to use the current name, with my own twist. For the family from County Tyrone, dating before division of Ireland, I use "northern Ireland" - note that I have specifically chosen to use a lower case n on northern - geographically correct, ancestry.com does not object, and I feel better, because "Northern Ireland" did not exist in 1864.
I have not yet been able to determine with certainty the county of origin of my other Irish branches, so I use Ireland, and ancestry does not override it. I hope someday to be able to pinpoint the others, and then I will use my own specific naming convention.