Hello @dcblack
I know it was five years ago - I've read it until a hour ago.... and Your Idea as a Feature for KM to be lockable is great - and I am inspired to have a solution to have my Macros locked from people who are not allowed to make any changes to the setup, too.
I don't know if you heard about an Application called iLock - made by OSXbytes
It is an Application to lock other Applications with very high secure Passwords... - want a password with more than 60 digits - no problem with this application .... and even the macOS Keychain has no problem to store it ....
it is also very automation friendly because its scriptable with AppleScript....
I am working for my self on a solution to lock KM and other apps like Terminal, Automator, Karabiner-Elements and so on... all apps whose are supposed to work together to keep my setup only edited be me...
I highly recommend for such a solution that you wouldn't only lock Keyboard Maestro Editor. Lock Terminal, too and for the Keyboard Maestro Library Folders I would recommend to use the build in FolderActionScripting - Feature of macOS to make it impossible opening the folder without a Password. but only on opening the folder not on writing to this folder(s) .... then you have the Security to KM you want to have...
you can even combine the FolderActions with KM... but use bash or python as script because it is very fast and can put the window of the folder to dock on a very fast duration and then asking you for the Password and keep it in the dock until your Password is correct using a Macro ...
In the macro you can even put an AppleScript for generating randomly Digit Codes whose can be send to your iPhone by using the Pushover Service so that you can use them to give you a self made 2FA solution.....
I am very sorry that I don't have a finished setup to share but if I am a 100% right that is what you can do - and use everywhere on your Mac where you don't want that others don't have Permissions....
If you don't have a solution like that - I hope this gives you an Idea ...
I will come back with a working solution when I have finished it for my own if you like ...
Perhaps there are some others here in this Forum they can help you if you have trouble to get it to work...
That was a lot of theory - I hope that I am right with all what I said
Good Luck and have a nice day
greetings from Germany