alas, macOS refuses:

     $ sudo ifconfig en0 ether 00:00:00:00:00:01
    ifconfig: ioctl (SIOCAIFADDR): Can't assign requested address

If you stash the IP/netmask/router IP you might be able to get it to work by setting a static IP on the connection with a 0 MAC address.

As always, ymmv.

On some equipment this may cause a broadcast storm, depending on how they implement things. Cisco equipment with some configs will send a packet to all the ports if it receives a packet and can't figure out where it's supposed to go.