Right Way Up,
Leading you to cross the threshold at 100ft if you follow the PAPIs in your average jet.
Let's not get carried away. For an average jet (what part) to cross the threshold at 100ft, even it was the best case 100ft eye-height, the PAPI would have to be installed 581m past the threshold. I very much doubt that it is.
Let's face it, if a runway is suitable for Cat D ops then nobody should have any trouble landing a cat C aircraft, regardless of the glideslope indications being used.
As I said before: brief what slope indications/guidance you are going to use, then use it the whole way to the exclusion of the others. It's pretty obvious that you are going to get yourself into a tiddle if you suddenly try to jump from the ILS GS to the PAPI at 200ft where the PAPI is not aligned, so why would you do it?
Changing to a Visual AimPoint (where is that?)
will unstabilise you unless the VAP is the same as the PAPI GPI or ILS GP antenna, which you had elected to use before swapping to the VAP, in which case, what's the point of using the VAP?