Hi Tyna,
As you have mentioned, the guidelines requiring a negative PCR test and not having to quarantine change on the 19th of July. As you are arriving on the 18th, the
current guidelines will apply, so yes, you would have to self-isolate. The guidelines are not specific enough to suggest that you can then come out of isolation the next day, we would suggest that you contact the
local Embassy for clarification.
Where are you coming from prior to landing in Dublin as there may still be rules and guidelines based on the country you are travelling from even after the 19th?
We hope this helps,
Martin