Since you started competing under China, you can stay with that if you want. However, if you do want to change you'll need to speak to Daniel. It can only be changed at the start of each calendar year unless it changed in the recent regulation update.
Also, none of your previous PBs will count as Irish until you break them again. So say you get a 9.00 average at this competition, and then change to Irish citizenship afterwards, it wouldn't be NR until you broke this at another competition.
EDIT: Relevant regulation:
https://www.worldcubeassociation.org/regulations/#2e2
And since this is your first competition of the year, and Ireland's first competition of the calendar year, you might be able to change for this competition. I don't really know the details but I'm sure Daniel will!