Carry a boxed bike on Irish trains?
 

I thought i might carry my bike directly off the airplane at Dublin onto an Irish train to Westport. In Westport grab a cheap room and cycle the west coast a bit, say 5 days. Return to Westport. This journey in September next.
Any known problems with the boxed bike on the train?

Please read the above as it is detailed and different train types have different rules. If you pass into Northern Ireland other rules apply.

Is the bike sonewhat dismantled inside the box? I'm not familiar with how bikes are carried on planes but assuming the box size is similar to that of a large suitcase then it should fit on the large luggage racks at the end of the train carriage.

It depends on how much the OP has collapsed it, sometimes the box can be pretty big or not much bigger than a frame.