You are exempt from first year VED rates, as long as exemption certificate is pressent and shown before the car is registered.
I claim exemption (through my daughter) on the Tucson (Motability vehicle) and pay £195 VED on my 220d GC, as its by far the cheapest way to do it. Exemption can only be applied to one vehicle (technically), so when I come to change the 220d, the Tucson will be returned or it will leave me paying luxury car tax on another vehicle, thats not strictly necessary. The Same applies HMRC VAT exemption on an adapted car.