Only thinking about that myself this evening Maxi as that's what i'll be doing that myself,when i was doing the opposite(private to taxi) back in 2015,i brought the RF111,VLC and my Taxi licence to my local motor tax office and they took care of it,received a new VLC from Shannon some time later with the new taxation class on it,
I don't know if my local tax office is open but as my car is still taxed (PSV)until the end of Feb i'm not going to effect that change until March.