I have decided to try and set up US Netflix account and hope people can answer a couple of questions for me so that I know what I am doing and don't stuff anything up!

Firstly I have an Apple TV and have changed the DNS settings (to unblock-us) in that so that Netflix now shows up and it thinks I am in the US.  All good there except that when I then try and login that way, it uses my iTunes account which then reverts me back to the NZ store and takes Netflix off.  So now I realise that I need to create a US Netflix account on my Macbook.  So then it seems that I need to change the DNS settings on there.  What I want to know is how reversible that process is.  When I go in to change the DNS settings they are grey which I have discovered means they are router settings.  If I change these does that mean that I am changing them on the actual router or just on the Macbook?  I am hoping it is just the Macbook.  It seems easy enough to remove them afterwards and reboot both the router and Macbook.  Does anyone know if that is correct?  

Also once I have created the US account do I need to keep the US or change I change them back and then just keep them to unblock-us on the Apple TV and everything will work successfully?

Many thanks for any help.