The rivet plastic clips that hold various panels on the 9-5 (like the carpet on the underside of the trunk lid) are ingeniously made.
I grew up working on cars with the plastic panel clips that have one-way barbs. You were lucky to get the clip out in one piece, and forget about that clip ever securely holding the panel again.
The plastic rivets on the 9-5 are made of two pieces. They not only hold tight, they can be reused.
The way to remove these rivet clips is to first press the center of the head with the tip of a small Philips screwdriver. The center will sink in relatively deep and the clip can then be pulled out with your fingers.
The SAAB part number for these rivets is 5127683.