VPI have now replied -- here's the advice:
"The down facing 1/4-20 bolt on your table is part of the original rubber
system. The whole rubber part can be unscrewed from the chassis by
pulling and turning the bolt counterclockwise. Pulling the bolt will make
the rubber smaller so you get less friction against the chassis parts and
turning it will unscrew the old rubber mount.? This should solve the
OK... Pmotz seems to have hit the target right on here. I tried it, using the 2 nut idea mentioned above to gain traction on the bolt (rather than gripping the bolt tread with a pliers) and with the full force of my arm on a wrench I could not get this thing to budge, it only gave as the rubber bushing twisted with the force but not further so I am not prepared to force it. I believe the down stud is joined via rubber to the bolt/stud that screws directly into the plinth, so you really need to turn the rubber join more than the bottom bolt - look at the replacement foot's insert to see what I mean, it's two bolts joined by a rubber midsection rather than one long bolt which you can turn by gripping directly. As you turn one end, the mid section rubber join flexes a little before the other bolt turns. Fine on a loose connection, but straining on the rubber when the joint is tight. VPI told me it was ok to wreck the tread as they could send replacements, and maybe the rubber would rip leaving me a chance to catch the upper bolt directly with a pliers but to be honest, I prefer to keep my TTable in working order - I am going to return these feet, more hassle than I am sure they are worth. If nothing else, VPI needs to get the instructions on this added to the packet - it is definitely not a trivial job for this version of the table.