We import and convert quite a few Japanese 4X4's each year.
In order to qualify as a commercial, the rear windows need to have panels fitted to render them opaque, (or to be removed and replaced with plastic of steel panels), the seats need to be removed and the mounting points for rear seats and seatbelts need to be welded over. You may also have to fit a load platform which covers the rear footwells, and a barrier to stop loads sliding forward and hitting the drivers seat. The savings can be significant in terms of road tax and insurance, but this needs to be balanced with the loss of flexibility and the reduced re-sale value.
I cant say if you can reclaim VRT on a car which has already been registered in ireland, but commercials qualify for a reduced rate of VRT on first registration in the state.