Hi rudderrudderrat,
Not sure which year you are referring to for the 747-400 but since 1997 I'm sure we have never used the PVD for landing.
The minimum RVR for take-off on the -400 is 150m (or 100m with PVD if notified in the take-off performance manual or CARD).
The minimum RVR for landing is 100m/100m/adv. There is no allowance for PVD.
Re-reading the tech manual, it does seem theoretically possible to use the PVD for landing, but you would have to push the PVD selector button below 5ft RA for it to unshutter. You cannot 'arm' it in the air.
Interesting to hear that you used it for landing on the TriStar.