BBBBAAAMMMPPP!!!
You're all wrong. Those covers are there for a special kind of clip. To remove the B Pillar without breaking it, you need to remove the cover and then remove the screw. Leave the clip in the sheet metal for re-installation. Attempting to remove the trim without removing the cover and the screw will BREAK the trim to the extent that it will have to be replaced.
Now, for the 64,000 dollar question:"Why is it there???"
It is a special attachment system that is used exclusively for roof rail airbags (the kind that drop down over the window glass in an impact. While they are not currently available, GM asked that we design the trim system to be "package protected" for them ... so they could add them with a minimal amount of change in the future.
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