I want to change dhcpd to assign a different dns server to clients.
Have you tried the DNS Server settings in Domains panel of Server Manager?
editing /etc/dhcpd.conf is an exercise in futility. I'm confident there must be some command I can feed setprop, but google hasn't found it and my random guesses haven't worked out.
config show dhcpd
will show you the current db config items set (which won't include dns server).
If you still want to do something not handled by the Domains panel in server-manager:
The fragments that are strung together to generate /etc/dhcpd.conf are found in the /etc/e-smith/templates/etc/dhcpd.conf directory. The one you are interested in is 25DomainNameServers.
Also look in the /etc/e-smith/templates-custom/etc/dhcpd.conf directory, as this is where local changes are held (unlikely that you have any there yet).
Then:
cp /etc/e-smith/templates/etc/dhcpd.conf/25DomainNameServer /etc/e-smith/templates-custom/etc/dhcpd.conf/25DomainNameServer
edit this new file to either hardcode, or use a new config item for the domain-name-servers (look at 25DenyBootp for an example)
when dhcpd is restarted the /etc/dhcpd.conf file will be regenerated from these fragments (using your /etc/e-smith/templates-custom/etc/dhcpd.conf/25DomainNameServer instead of the standard one)
Good Luck
Trevor B