I think I know what you are talking about. It sort of looks like a stop of some kind.
Yes! It comes off or out or however you want to look at it. You can just grab it and it should come right off. Actually, under this piece of rubber is where the outter mounting points are for the stock wings found on our cars. You could also use the opening as a guide when drilling your holes. (Man! That made me ~~shiver~~. The mear thought of drilling holes in my car!) I am almost certian that the design is the same across all model years.
If you have a wing with three mounting points, then look to the center of the trunk lid. You will see a oblong openning. This is your center mount point.
Hope this helps and good luck.