Can regular government workers do that, or just actual diplomats? If the latter, just go for their assistant.

Under the Vienna Conventions, only people with diplomatic rank have full diplomatic immunity. Administrative and technical agents do have diplomatic immunity, but only for actions taken "in the course of their duties."

But it wouldn't matter: documents and archives of the state are inviolable no matter where they are. And the property of a diplomatic mission must remain free of search and seizure.

I can't wait for some Irish cop to start a massive diplomatic incident because some embassy worker happened to be in the wrong neighbourhood.

I think this is more likely to bite as it pertains to Ireland as a friendly business environment than it does to Ireland as a diplomatic partner.

Yeah but the diplomatic disaster would have far more entertaining visuals.

I had a diplomatic passport for many years as a kid. It was definitely handy in our case as cops were quite corrupt where we were living and would try to con us out of money all the time. I don't know how far it'd go in court or under a serious warrant but in practice they always left us alone once we showed our passports.