I don't know for sure, but I would say that since netmask and gateway etc are changing, you will need to edit the ifcfg-ethX:Y files and the hosts files etc, restart the network to make sure you still have connectivity, then use the plesk reconfigurator ( /usr/local/psa/bin/reconfigurator ) to change the IPs on all your domains in one go, either automatically or via a map file.
Console access is essential in case you make an error (or make sure someone at your data centre is on hand to connect a keyboard and monitor to fix things if they go wrong).
After the reconfigure, check the list of IP addresses in Plesk to make sure it looks correct. Be sure also to check as many DNS records as you can after the reconfigure to make sure all is well there too. Check subdomains and domain aliases as well.