commercial vehicles get different tax and insurance rates in ireland... There are other laws outside of the uk lads.. That said however i would make sure you find out from the revenue what needs to be done and make sure everything is 200% above board.
people do this with jeeps and other hatches all the time. Remove rear seats and floor out the back and the vehicle is a commercial and can legally get cheaper tax. I think unless you are from ireland or know irish law you should probably not be commenting on this guys question. As said already check with the revenue mate.
bear in mind if you are running a vehicle as a commercial it must go for a DOE instead of an NCT... the DOE must be done every year!
My mother gets her jeeps in commercial guise as she is a director of my fathers company and she can get them VAT free, the diesel can be claimed as an expense and the annual tax is a lot cheaper. The down side is it cant have back seats though.
I also know of people bringing in 7 seater jeeps from japan and removing the back seats flooring them out and turning them into commercials for tax purposes. Well worth doing if you dont plan on carrying anyone in the back.
Again I would double check all the legalities before doing this. There might be something on revenue.ie about it or oasis.gov.ie