First you'll have to diable the clan in ip-interfaces. You may also have to disable anything that's using the CLAN, such as ip-services and communication proccessor channels. Once you change it, you'll have to change all of the screens that reference that name, such as ip-services, ip-routes, ip-interfaces, trunks for DCS, and communication processor channels (there may be more, but that's all I remember off the top of my head.)