Follow this procedure when moving a FreeBSD box from one IP to another.
Change
DNS to new IP address. You'll want the TTL on the domain to be pretty short, so that the IP address updates quickly.
Change ifconfig settings in /etc/rc.conf
Change /etc/resolv.conf
Change /etc/hosts
Reboot the box (best, to test the new ifconfig line), or do a manual ifconfig to the new IP.
TEST everything
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