I think the confusion has arisen because you can import a car you have owned for 6 months or longer into Ireland with a VRT exemption if you are moving your permanent residence from the UK to Ireland. You have to prove to the Revenue that you are actually moving, we had to show solicitors letters and property particulars about the house we sold in the UK when we moved over here.
Apart from that I dont think you can get away with not paying the VRT if your main residence is in the Republic. Unfortunately.