On sporting, the knob is moulded as part of the push down reverse mechanism, so doesn't come off without cutting. i wouldnt advise this as its a pain in the arse findin one to fit afterwards. i did it , then ended up buying a brand new one from fiat for £40. waste of cash.... i think so.
Its easier to re trim the existing one, take off the leather (u'll have to cut the stitching), use this as a template to cut whatever material ure gonna use, then crack out the old needle and thread. piece of **** if u can sew, if not get mother to do it.