I prefer using external keyboard with my MacBook. When no external monitors are used, a typical setup is placing the keyboard above the internal one, so I can still use the internal touchpad.
But sometimes the external keyboard may press some keys of the internal keyboard. There is a solution to disable the internal keyboard, but it is tedious to run the command manually.
# Disable, ignore the warning
sudo kextunload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/
sudo kextload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/
Fortunately, Keyboard Maestro supports executing scripts when a USB device is attached or detached.
I have created two macros to enable and disable internal keyboard.
Before the macros can be used, you must setup sudoers to allow running the command without password.
$ sudo visudo
And append following line to the file and save it.
%admin ALL = NOPASSWD: /sbin/kextunload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext, /sbin/kextload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext
Then restart sudo session
$ sudo -K