[jdmass]

The plastic parts are for one-use only. There is no way that I know of to remove them for reuse. The mudflaps should have come with its own fasteners, including screws, screw retainers, and plastic pins as I showed in the pictures. The official instructions that I attached (PDF file) to my post show which fasteners to throw out and which to keep.

To remove a plastic pin-type fastener, I pried it with a screw driver to get enough of the edge up to be able to grip it with a pair of pliers. In some cases I could yank out the entire pin, in some case, it broke and the remaining end fell into the interior of the wheel well. No real need to worry about it as it wasn't being reused.

You commented that the hole was damaged. Not so. There are some scratches on the plastic from prying up with the screw driver (probably should have been a little more careful), but these are completely hidden by mud flap. The hole itself was not altered one bit. I suspect that this type of effect is pretty normal, even if installed by the dealer, because it is never seen.