Does KM have an action to open another KM macro's (editing) window?

Not looking to open the palette as I don't want to execute the macro.

Just want to end a macro with a KM action to open another macro's editing window.

Is this possible?

You mean an action go to and edit a specific macro?

Yes, you can do that with the AppleScript:

tell app "Keyboard Maestro" to editMacro "Name or UUID"

UUID is better since it will always be unique and will not change if you rename the macro.

You can get the UUID of the macro with the menu command Edit ➤ Copy as ➤ Copy UUID.

The AppleScript can be executed with the Execute an AppleScript action.