Swap CMD and Alt only on external keyboard On my external mechanical keyboard the Super/Windows/CMD key is between Ctrl and Alt, but on the Mac keyboard it's between Alt and Space. 

Can I swap CMD and Alt only on the external keyboard?
There is a section dedicated to this under  → System Preferences → Keyboard:



Open Modifier Keys… and reassign them from here:



These settings are specific to each external keyboard you have connected. They will “stick” between reboots, as well as whenever you unplug an external keyboard and plug back it in.