Re-qualifying for Jobseeker's Benefit
If you have used up your entitlement to Jobseeker's Benefit (JB), you may re-qualify by working and paying the appropriate PRSI contributions for at least 13 weeks. If you are working and getting JB, as in the case of systematic short-time workers and some part-time workers, the 13 weeks paid contributions can begin once you have claimed JB for 156 days.
You must have suffered a substantial loss of employment to re-qualify for JB, unless you are a casual worker. If you have lost your job you will have suffered a substantial loss of employment. If you are a part-time or systematic short-time worker DSP will look at your pattern of employment over the last 13 weeks or another representative period to find out whether you have suffered a substantial loss of employment.
For example, if you are getting JB and working 3 days each week as a systematic short-time worker or a part-time worker and your employment pattern has not changed during the course of your JB claim, you will not have suffered a substantial loss of employment and will not re-qualify for Jobseeker’s Benefit.
However, if your JB claim ends and your 3 day week working week is then reduced to a 2 day week, you will have suffered a substantial loss of employment and may re-qualify for Jobseeker’s Benefit.
http://www.citizensinformation.ie/e...nts/unemployed_people/jobseekers_benefit.html
As regards your last question it's entirely up to you whether you make a claim for JSA or not and will have no effect on any future claim.