This KB describes on How to change a Cpanel servers main IP.
Make sure to take a backup of all the files mentioned in this KB.
1: edit /etc/sysconfig/network-scripts/ifcfg-eth0 and replace old server IP with new IP // assuming eth0 as the primary Device
2: connect the server with LAN IP or IP-KVM
3: restart eth0 device
>> ifdown eth0
>> ifup eth0
3: Edit the following files
>> /var/cpanel/mainip //replace old IP with new IP
>> /etc/ips //replace new IP with old server main IP
>> /etc/hosts //replace old IP with new IP
4: update Cpanel licence
5: Ran the following script to update domains IP’s
>> for i in `cat /etc/trueuserdomains |cut -d: -f2`; do /usr/local/cpanel/bin/setsiteip -u $i newIP; done // assuming all domains using the same shared IP’s