How can I disable the macbook keyboard with Shift key held down on a password protected macbook?
Disable keyboard:

sudo kextunload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


Enable keyboard:

sudo kextload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


For manipulation, you can use the virtual keyboard:
System Preferences > Keyboard > Keyboard > Display panel "Keyboard" and "Symbols" in the menu bar