Changing a wifi signal

I am using a Netgear R6400

Pretty simple, I have a cable box in my house that has wifi. Lets call that Wifi "HOUSE". Then I ran a cat6 out to the back, which is an office, Let's call that  WiFi "OFFICE".  So same network in house as the office. Easier being on the same NETWORK, for internet, Shared Drives, & Surveillance gear.

I put the netgear R6400 in my office and that puts me on two differnet networks.

Can I make the R6400 the same network as the Cable companies WiFi modem in the house. This way, If I'm in the house or the back office I will still be connected to the same network.

Can this be done??

If NOT, is their a WiFi Router that Netgear makes, or is there something I can do???

Thank you