Dan, if you mean that you are connected by dhcp by your cable company (if this is the case) you can change the DNS everytime you want to, in your router or/and if you donīt use a router in your network preferences.
DNS,s are not tied in a local network if you mean internet from a cable company. Perhaps you didnīt find how to do it or you are connecting in a different manner.
I only wanted to help
