Update:-
First, let me say thanks to everyone for the helpful replies.
I decided to get a quote from Vincent Byrne, Osbornes and McDowells. Well that was the idea. My first port of call was Vincent Byrne, South Anne Street. His quote for re-sizing my wedding ring (no need to put a piece into it) and for putting a piece into the engagement ring band - 2 sizes bigger?????? 20Euro!!! How could I pass up on that, wearing the rings as I type.
Cheers