Can Royal Icing be sanded smooth?
Are you covering a cake with royal icing? If you're not getting a smooth finish, you need to ice it the traditional way, that is, ice it with a layer of firm peak icing, then 24 hours later, ice it with a layer of medium peak icing and then lastly ice it with a soft peak.
If you're not getting a smooth enough finish on your royal icing you may need a softer peak.
If you are doing a dummy cake, then yes.