I am going back many years here but in another time I was working with the Australian Dept of Civil Aviation Navigation Aid Calibration Unit. This involved flight testing of ILS and also T-VASIS. Although the ILS was flown down to 50 feet to look for aberrations below the nominal Cat 1 of 200 feet, it was not intended that aircraft would follow the ILS glide slope below 200 feet since measurements below 200 ft were not always reliable.
I am sure measurements are more reliable now with the advent of lower DH. On the other hand the T-VASIS was only flight calibrated to 200 feet and it was never intended to be used below 200 feet because of lateral siting.
VASIS and PAPI are visual aids to give an accurate visual slope from 4 miles and again it was never intended to fly an ILS in IMC to 200 ft and then use the PAPI/VASIS below that. In any case if the aircraft is stabilised on the ILS at 200 feet there should be no need to further "fine tune" below 200 ft as the aircraft is within seconds of crossing the fence and heads should be up unless Cat 2 or 3 ILS.
Attempting to switch to a PAPI glide path indication from an ILS at 200 feet is asking for trouble as the siting of the PAPI may not be the same position as the ILS glide slope transmitter. In other words don't make things unnecessarily complicated when there is simply no need.