Hello
I believe there is no change in the hostname of the machine where SAProuter is running.
In that case SAP will only update the IP address of the server where SAProuter is running.
I don't think there will be two IP addresses (old and new) maintained by SAP.
You just need to check under the "System Data Maintenance" at http://service.sap.com/system-data
and see whether the new IP is shown under the SAP-Router section for all the systems.
Back to the SNC part. If the saprouter is configure with the SNC functionality then the SNC name is based on the host name of the SAProuter and not with the IP.
If there was a change in that then SAP would have provided you a new SNC name for the SAProuter when you notified them about the change in the IP address.
Like I said before, any references to the old IP SAProuter address should be modified with the new one.
Eg: OSS1, any SAPNET RFC's, SAP router saprouttab configuration etc.
Regards
RB