Need to spoof MAC of ethernet-connected wifi adapter

I got a directional wifi adapter at a little beach cottage in order to make a better connection to the router in the main house. Even though the handshake works well, I am not getting the router to give me an IP address, because I'm using MAC filtering for security. I can just barely make the connection without the directional adapter, but the signal is weak and keeps dropping.

So does anybody know how to send the ifconfig command or whatever would work to the ethernet connected device to change its MAC for the handshake?