Which Spark router?

No. The Chromecast is set to only use Google DNS. The only way to "change" the DNS for this is to redirect Google DNS to another DNS provider. The router you're using doesn't support this.

If you're trying to unblock Netflix in another country then you need to follow your providers static route settings (as in, whatever DNS provider you're using). No, you'll not get help around here in public space on what to put in, and where, you're going to need to consult to your DNS providers help pages on that one.

Just spoof google DNS IP addresses on your own network :)

got a Huawei HG659. and using dns4me service aswell