There are 2 types of temporary licence in ROI - a 30 day and a 100 day. The 100 day (per year) is really a trial community radio licence. The temporary mostly music based stations (the most well-known one being Christmas FM) are 30 day licence, which is much easier to obtain and doesn't have all the difficult requirements mentioned above by Peter of the 100 day one.

There is for example a 30 day temporary FM licence on in 4 Irish cities presently, Gravity Hits - which is effectively a 'relay' of the station on DAB+, I assume to bring it to the attention of people without DAB.

Incidentally
people may recall (after UCB relayers ceased using the transmitter on 549kHz around the mid-2000s ) a temporary licenced country music group operated a 30 day licence over 15 weekends (Sat&Sun) using relatively high power 549AM on what later became the Spirit AM site.

Funnily a google search seems to find nothing about the existence of the temporary country music station on 549 (maybe I am not searching right?) but I'm sure a few readers here would remember it