modify ip of rac interconnect and vip

The VIP are registered as a highly available resource within the Oracle Cluster Registry (OCR).
If you want to use different VIP's than the previously configured you need this Metalink Note 283684.1 How to Change Interconnect/Public Interface IP Subnet in a 10g Cluster
Be aware of the following bug: 4500688 - THE INTERFACE NAME SHOULD BE SPECIFY WHEN EXECUTING 'SRVCTL MODIFY NODEAPPS' that is not described in the mentioned Metalink note above. This means that it is better idea to modify the VIPs by explicitly specifying the network interface name, for instance: srvctl modify nodeapps -n mynode1 -A 100.200.300.40/255.255.255.0/eth0