Traitor knives don't have skins but normal knives have skins
Your best bet is just to suggest that you can equip different skins for your traitor knife as knives will likely never be added to any other role.
Replace the crowbar with a CSGO knife
No. It would cause too much confusion for new players as the knife is pretty much on every server a traitor only weapon. Although there was that brief time when we had crowbar skins wasn't there? Maybe that should come back.