What OS and VM are you using? If you aren't adding a new IP and only updating the I'd just edit one of the two files depending if you are using a Debian flavored OS or a Redhat based OS
With Debian based (e.g., Ubuntu, Debian, Xandros, Mint) the change the settings in /etc/network/interfaces followed by:
service networking restart
RedHat based (e.g., Fedora, RHEL, CentOS) then you'd update /etc/sysconfig/network-scripts/ifcfg-eth0 and then run
service network restart
Not sure if this is can even be updated outside of the OS. With xenserver I always just update in the OS.
As far as other things you would check it would depend on what subnet are on. I'm guessing since this is in RFC1918 space you are probably on 10.10.10.0/24 and so you'd be able to add it if no one else was using it.