It is my understanding that you can approach the council and they will consider on a case by case basis, usually they will extend the clawback period ie if it is 20 years they will extend by the amount of time you wish to take a break from the scheme, so it will be 22 years for example.
Did you have your apartment valued at 290K? Chances are that the value has gone down from the value at the time you bought, as it has for every other apartment in the country.
Also you can apply for a 99%/1% share under the shared ownership scheme with Dublin City Council, mine originally was 50/50 but recently got it changed, the Council ofcourse don't tell you these things, you have to learn about them on forums! Your mortgage repayments will go up ofcourse.