MAC address filtering with extender

I am successfully using MAC address filtering on my main router (a Netgear product). On that device's setup page, I can manually enter the addresses of each device I want to authorize.

I am also using the AC1200 extender. Everything that connects to the extender gets passed to the main router with the SAME MAC address, not a unique address for each device that is being relayed. So, I have added the single MAC address coming from the extender to the authorized list on the main router.

This behavior is different than with my old extender, where the virtual MAC address for each device was distinct (it was a variation on the original MAC address for each device).

But now, everything that connects to the EXTENDER can get onto the main router.

So, I want to turn on MAC address filtering at the extender, limiting what can connect to it.  The setup site for the extender allows this to occur. However, there is no way to manually enter addresses. If MAC filtering is turned on, it limits access to whatever was connected at that time. But with many devices that will access the extender, I can't connect all of them at the same time to turn this on!  There is never a time that every person in the house is home with all their devices at the same time, all connected to the extender at the same time. For example, I have guests that visit once in a while and I'd have to turn MAC filtering off every time they are here. All of my out of town guests are never here at the same time, so it would be impossible to connect them all simultaneously. This software design is a PITA.

Why can't I manually update the list of allowed devices on the extender (by going to mywifiext.net) just like I can when I go to the main router through routerlogin.net?