@Tomp28110 

It will work, but you will not have a continued mesh network so if a device jump from the extender to the Deco network you will have a moment where there is no internet as it switches. 

Alternatively, you can name the extender a different name, just so you know which network you are connecting to or not have to deal with your device switching back and forth causing constant network interrupts.

@Tony 

Thanks Tony