I have remapped the carriage return to a different command (ctrl + space) but this isn't recognized at the mac locked screen -- there is no response to this trigger. Is there a way for the mac lock screen to recognize KM keyboard mappings?
Here's a post from Peter addressing that, to a degree.
@peternlewis : it seems you're best placed to answer this. If the screen is locked, will a KM keyboard command that remaps a the carriage return key be blocked? Can I set my system to allow for these or is there another way around this problem?
If the Mac is locked, then you are essentially outside the user environment, so I would not expect Keyboard Maestro to see anything or be able to do much of anything.
I don't think Apple wants apps to be able to intercept keys during the unlock or login process, because that would allow app developers to view the user's password.
Now that I think of it, I think that also could mean that KM's hotkeys probably don't work when macOS is asking the user for his password, even when the user is already fully logged in. I never thought of that until now, so I'm not positive this is true.