It's not what you're asking for, but in case it's of use and you didn't already know:
"... the %MacUUID% token is a unique ID for each Mac, and can be used to test which Mac the macro is running on"
– manual:Macro Syncing [Keyboard Maestro Wiki]
Update: I have just seen this relevant discussion: How to make “disabled on this Mac” default to ON for a particular group?