A preset locally administered MAC address is used as the BSSID of the AP. Changing the MAC address of the Wifi interface doesn't affect this.
The Internet Sharing in System Preferences invokes
which then communicates with
wifid via IPC to change the mode of the Wifi interface.
Problem: Internet Sharing only works when Security is set to None in Wi-Fi Options. Version: macOS 10.12.4 Model: MacBook Air (13-inch, Mid 2011) Wi-Fi: