Any Engine Launch triggered macros are easily dealt with since you control their behaviour.
There is no “Pause Engine” because what it means would be different to different people.
- Should the application/window switcher keep working?
- Should the clipboard history keep recording?
- Should the list of running applications and their orders keep updating?
- Should the web server keep running?
- Should the web server keep accepting remote clipboards?
- If the Engine is paused, how can you reactivate it?
- Should just UI triggers be paused? What about remote or timed or application change triggers?
- Should the status menu still work?
etc.
If you want specific macro groups to be inactive, inactivate them using the existing methods.
If you really want to stop the engine, then quit the Keyboard Maestro Engine, and launch it by some other means, and accept that all of its facilities will be missing.