there are
a no. of rivets holding down the facia over the rearward
part of the trunk seal. I need to remove this plastic
facia to pull off the seal. I have run into these plastic
rivet like fasteners before. They have a ferrule with lip
that holds the facia down and a center mandrel that expands
to hold the little ferrules in place. The center mandrel is flush with the top of the ferrule. Do I push down on the center mandrel?..to disengage the ferrule so I can get the ferrules off to remove the facia? No undercut or groove to pry the mandrels out from the center of the ferrules so presume you push down to disengage these fasteners?

The easiest way is to drill the centre of them and pull it out with a screw. The fasteners cost pennies from the dealer. Part number is 51 48 1 905 599.