On my server they are in /etc/sysconfig/network-scripts/ifcfg-eth0
and changing it there and issuesing a service network reload will work.
Likewise you can use
ip a add 0.0.0.0/0 dev eth0
to add, change and remove them. however I would recomend against doing this as when you reboot MWG will change all the settings back again. I'm sure you can make it persistant if you try, but unless there is an overiding reason why you would want this long term rather than to just suffle things in the backround whilst you do something I'd use the UI.
derr on my part. I read that wrong....
Tris' commands should work, I use ifconfig:
# Temporarily configure IP address (will not persist through reboot)
ifconfig eth0 <desired IP> netmask 255.255.0.0
You may also want to set the default gateway sometimes, to do this you can use the following, this will temporarliy set it as well:
ip route add default via <default-gw-ip>