I presume you have an AIB split mortgage?
What term is left on your mortgage?
You say it is your lovely home? Will you be staying in it forever or might you need to move or trade up or down?
You don't need to make any decision now. There is no advantage in paying money off now. Wait until just before the 5th anniversary to decide if the 70/30 repayment is worth taking. How many years will be left on your mortgage at that stage?
Lots can change in 5 years. Although you might think that this is your final home, the situation may be different in 5 years.
If things get a lot worse for you, maybe voluntary surrender and bankruptcy might be an option. You will not want to have paid off some of a loan unnecessarily if this happens.
It's very important that you stick the the revised agreement or else you could lose it. So if things are still a bit tight in 5 years' time, but you have access to a family loan, it may be better to keep it in reserve to make sure you pay your active mortgage.
Brendan