Denying MAC Address Access

Trying to limit device access to only the Guest network.

If I block a MAC address on my Verizon Gateway Router, will that MAC address still be able to log on to the WIFI EX3700 being used as an Access Point only for the Guest network?

I ask this because I accidentally revealed the password for my entire network to a user that should only be on the Guest network. I have over 40 devices so do not want to change password. I want to limit his access to only the Guest network.