The Surfboard Central is always updating and getting better, for the moment this feature is not available, but of course you can request the app to provide the Web Manager access, and then on the GUI, you will follow to the option Connected devices and you can create and blacklist of MAC addresses that you do not recognize, so those one will never have access again to your network

Hope this information helps you and also this articles could be useful for you

https://arris.secure.force.com/consumers/articles/General_FAQs/SBG8300-Parental-Control-Block-Internet-Access/?l=en_US&fs=RelatedArticle

https://arris.secure.force.com/consumers/articles/General_FAQs/SBG7600AC2-Restrict-Wi-Fi-Clients

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