Warging is not a synonym of skinchanging. Warging is a subcategory of skinchanging. It exclusively refers to skinchanging into a wolf. You cannot warg into a dragon or a person or a raven or a cat or anything other than a wolf. Someone who skinchanges into something other than a wolf but never a wolf is not warging and is not a warg.
All wargs are skinchangers, but not all skinchangers are wargs.