If you change the following settings; Hostname, IP Address, Subnet Mask, Gateway Address, Time Zone, NIC speed, SMTP server, Primary DNS server and/or Primary NTP server. Your License MAC gets regenerated and thus, you need to contact Cisco to rehost your license. I believe, Cisco moved the licensing service to a new website. You should be redirected to the new website by going through the old website (www.cisco.com/go/license).
What do you mean by SIP Router? Are you talking about a SIP Proxy server? If so, please confirm... do you have UCCX or UCCE?