Hello
You need to make sure that all the RFC's from the other systems pointing to these systems are working fine. If they configured with the host name then it should be fine.
The IP address of these systems should be updated in the hosts file of all the systems where the old IP address is maintained.
Once the IP addresses are changed just make sure that the transport directory is accessible for SAP and also RFC's are working fine.
If the saprouter is installed on the server where the Solution Manager is installed then you need to update that with the SAP Support through an OSS message.
Once that is updated you need to correct the saprouttab file if required with the new IP address.
Regards
RB