Jim B
It depends on the manufacturer however most of the dealer added molding glue on with special 3M glue. Nonetheless, if your concern is that you may want to take them off one day... the glued on ones are just as bad because if you take them off, it will be hard (but not impossible) to remove the glue and depending on how long they were on for... the paint under them will likely be darker than the rest of the bumper. Options like this seem to make sense but in a way they are counterproductive. The entire point of them is to protect your bumper from damage however adding them to your car almost insures they will get damage just from being installed. Personally, I think options like this are just another way to make a few bucks for the dealers. I would skip it.