Just so we're clear - your wanting to fit plastic arches to a model of Golf that did NOT originally have arch trim? i.e. there are no holes at all already in the arch?
Whatever is happening you can't just pull the rivets out - they are pop rivets - the need to be put in using a special tool (simple, but special). When they go in they 'pop' or in other words explode outwards inside the arch, kind of like a fish hook effect, easy to go in, impossible to come out - you'll have to drill any old ones out carefully.
