Actually Jer i don't think they did. The referendum on articles 2 and 3 was quite played out in Ireland at the time. Certain sections of civil society argued that to vote against the change was also a vote against "Peace." I don't think that anyone in ireland rejected the idea of a united Ireland beacuse the change in the constituion actually allowed anyone born on the 'Island of Ireland' the right to be an Irish citizen. Article 3 expresses the aspiration to a united ireland when accepted by 'both' sides. Hardly a rejection.
From article 3.
1.It is the firm will of the Irish Nation, in harmony and friendship, to unite all the people who share the territory of the island of Ireland, in all the diversity of their identities and traditions, recognising that a united Ireland shall be brought about only by peaceful means with the consent of a majority of the people, democratically expressed, in both jurisdictions in the island.