1. Make sure you have followed http://devwiki.pfsense.org/DevelopersBootStrapAndDevIso and have a working ISO build first (very important!)
2. Issue these commands in your FreeBSD 7 shell:
cd /home/pfsense/tools/builder_scripts/builder_profiles/ cp -R pfDNS MyAppliance && cd MyAppliance
3. Issue this command and then edit the files that it outputs changing pfDNS to whatever you like.
grep -R "pfDNS" * | cut -d":" -f1 | sort -u
4. Build your appliance (issue these commands in your FreeBSD 7 shell):
cd /home/pfsense/tools/builder_scripts/ cp builder_profiles/MyAppliance/pfsense_local.sh . ./build_iso.sh
5. Test your ISO. It will be in $MAKEOBJDIRPREFIXFINAL/ ... Check pfsense_local.sh for the variable definition (defaults to /tmp/builder/)