The pillion seat pad is no longer available as new from Honda (according to one well known local supplier here), but can be found online if you know where to look. There will be plenty of 2nd hand ones available though.

It is attached at the rear by a small bolt that goes through a metal bracket under the tailpiece. The hole is visible thought the tapered groove in the top tailpiece. At the front, it is held down by the strap/handle (which is available new). The ends of the strap are in turn fastended to the underside of the black plastic 'glove box' inside the seat hump.

In regards to marking the paint - they will do that, mine has rubbed at the gold stripe decal on my Rothmans '21. I have just obtained another top fairing to replace the old scuffed one, and will be putting the pillion pad into storage.