I'm sorry, but we never suggested that you make any changes to the Netgear modem/router.
We told you that you could connect an AirPort Extreme to the Netgear modem/router using a permanent wired Ethernet cable connection and set up the AirPort to provide a WiFi network. This will work fine, and no changes at all to the Netgear modem/router are required.
We also mentioned that you could connect a second AirPort to the first AirPort using a wired Ethernet cable connection if you needed more WiFi signal coverage in another part of the house.
Just ignore the WiFi signal of the Netgear modem/router, or use it as a "guest network".
If you don't want the Netgear modem/router to provide a WiFi signal, most modem/routers will allow the WiFi to be turned off. The product still operates as a wired modem/router when you do this. An Apple router can do this. I assume that the Netgear......which is a lot more sophisticated than the Apple.....can do so as well.
In other words, turning off the WiFi does not turn off the routing functions of the product. Nothing changes, the Netgear just stops broadcasting a WiFi signal.
It sounds like you were trying to configure the Netgear modem/router to operate only as a modem.....not a router. There is really no need to do this, even if it might be possible.
It is your call as far as any changes or modifications to the Netgear modem/router. We will not be able to help on that.