The body side moldings were an option on all C5s. To double check, take a look at the C5 Specification pages here at that CAC. As for how they're attached, although I can't verify it, I'd venture to agree with Tom.
There is a way to remove the BSMs.
1. Monofilament or dental floss
2. WD 40
3. Start at one end of the BSMs and spray some WD40 on the edge of the BSMs and gradually work the monofilament or dental floss on the adhesive side of the BSMs and they will gradually come off. Take your time!!!!!!!!!!!