Hi @DanThomas,
I was looking at this paragraph that Peter wrote and it made me wonder whether your Import Manager should have an option that incorporates his security point (my bold):
...if you import macros the macros can run immediately (for example , if triggered by something like Periodic Every Second), so if you are importing a macro from an untrusted source, it can execute something pretty much immediately - this is something to keep in mind if you don't trust where you are getting the macros from. You can safeguard yourself by relaunching the Keyboard Maestro editor (as above) and then quitting the Keyboard Maestro Engine so no macros are run, and then importing the macros. Then you can look through the macros and verify their behaviour and/or disable them and then relaunch the Keyboard Maestro Engine.
I've used MIM for the first time today on a few different macros, and so far it works well!
Peter's post is here: