The unique value is required at the time that domain control is validated. Therefore, if you add a new domain name when reprocessing a multi-domain certificate and wish to use the DNS CNAME lookup or HTTP/HTTPS file lookup validation method, you will need to create a new CNAME or validation file, with a new unique value. If you have prevalidated a domain name via the CNAME or File Lookup methods, a new DNS record or file with a new unique value is not required when ordering a certificate for it.