Well the people of Ireland have said "No" on many occasions, so not sure which one you are referring to.

But in the case of the GFA, they voted 94% in favour of changing the constitution to accept the provisions of the GFA. And that included dropping article 2, which claimed the island of Ireland as the national territory.

So in that respect they are very much agreed on the process. Whether at the time they would accept an United Ireland is another thing. My own feeling is probably not.