OK, so you have €75k on a tracker of say 0.8%.
If you move this to another home, the rate would increase to 1.8%. You would pay the market rate on the balance, if any.
With a low LTV you can get a mortgage at 3.1% which should fall.
So if you lose your tracker, you will lose the difference between 3.1% and 1.8% or around 1.3%.
1.3% of €75k is around €1,000 a year.
As it's a tracker, you are paying down the capital at a very fast rate - so it will probably fall to around €500 interest differential in 5 years.
In other words, forget about keeping the tracker and just make the move which is right for you.
If you sell your home, you will probably have 6 months to buy in Cork and keep your tracker.
Your wife can rent a flat in Dublin if she is here only 2 nights a week.
Brendan