Hi,
If u r making IP changes in the same subnet then u can do so using ifconfig command:
ifconfig hme0 <new IP>[hme0 is the N/W interface]
However to make these changes permanent, edit the file /etc/hosts and replace old IP for the server with new one.
But if u r making changes in diff subnet then edit files:
/etc/hosts,/etc/defaultrouter,/etc/netmasks
In all these replace old values with new ones...
I hope this helps.....