@MiamiDadof3 

I know iOS has the feature, but not W10?

I assume the routers sees it as a new connection when it gets a MAC Address it didn't see before. I base this on the fact that my PC's (W10) will always get the same DHCP IP Address, the order of those handed out always be the same EXCEPT for our iPad's and my iPhone. I verified this by turn Private Addresss OFF on those units and they again get the same IP Address as they originally had (I assume, but now always the same).

That said, I assume that the setting ACCESS CONTROL under SECURITY and use WHITELIST which would have the presently connected devices, would stop any device with a new MAC Address. Once that happens, you could then ask that Private Address (it is per Network) be turned off, and the you'd permit it to connect. May have to 'play' with the other settings that might have different MAC Addresses though in Parental Controls. I think once Private Network is turned off, the true MAC ADDRESS of the device is used.

Just my thoughts on this, I could be wrong. Guest Network would have the same restriction and it could cause you some problems of always needing to allow guests in.