I use Karabiner to swap the `Command` and `Option` keys when I have an external keyboard plugged in. It's so annoying to have to manually switch the profile, though, so this script does it for me automatically, whenever I add or remove the keyboard (or when the device wakes, in case it was added or removed while it was asleep).

HammerspoonKarabinerKeyboardSwapper.lua

function switchProfile(profile)
  local karabiner = "'/Library/Application Support/org.pqrs/Karabiner-Elements/bin/karabiner_cli' --select-profile "
  print('Switching profile to "' ..  profile .. '"')
  hs.execute(karabiner .. "'" .. profile .. "'");
end

function isKeyboard(device) 
  return string.find(device["productName"], 'Keyboard') ~= nil
end

function usbDeviceCallback(data)
  if (isKeyboard(data)) then
    if (data["eventType"] == "added") then
      switchProfile('External')
    elseif (data["eventType"] == "removed") then
      switchProfile('Internal')
    end
  end
end

function runCheck()
  local usb_table = hs.usb.attachedDevices()
  for index, usb_device in pairs(usb_table) do
    if (isKeyboard(usb_device)) then
      return switchProfile('External')
    end
  end
  switchProfile('Internal')
end

runCheck()

hs.usb.watcher.new(usbDeviceCallback):start()
hs.caffeinate.watcher.new(runCheck):start()