I am not sure I understand. Families are associated with a clan of living and desceased people, not tartan designs woven into pieces of cloth. Clan is from the Gaelic for "children" and the members were all said to be descended from a single progenitor (at least at the beginning of such things), thus clan is family and family is clan. So, either you are associated with a clan or you are not. If your family is indeed associated with a clan, that IS your family, and there is no need to design another tartan not approved by the chief of the clan. If you are not associated with/a sept of, etc a clan, you can make up anything you want. It will be known as a fashion tartan, not a clan tartan.