CIE, certainly, but the GSR maybe not as much. However, it was the GNR that started the pop head rivets on their locos, for the sole reason the were a hell of a lot simpler to take out than the countersunk rivets.
Even the 800s originally had countersunk rivets.
In my opinion, despite being a pain in the a^$<'*#$ to model, The (three thousand:p) rivets are a major charictestic feature of Irish locos in the CIE period