Hi Lee,
Yes, you can change the entry after installation
by using the following CLI command:
CLI > set network dns
Enter the IP address of the DNS server that
you want to specify as the primary DNS
server. Enter the IP address in dotted
decimal format as ddd.ddd.ddd.ddd.
Consider this field mandatory if DNS is set
to yes (DNS enabled).
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/install/6_1_1/install/cmins611-cm.pdf
Hope this helps!
Rob