Ahhhh.... I had completely missed that as a way of quickly adding Macros to the Trigger Macro by Name` initial list, I was scrolling down the huge list of Macros to find them... This is really quick.
So, this really does make a particular Trigger Macro by Name Macro a bit like a conflict palette with a list of favorite Macros... interesting. It might not exactly match your needs @kevinb but I am going to play with it and see how practical it is. Thanks @kevinb for starting this topic.
It wasn't quite to my taste, no. 
No, it's good, and I knew about it, so went to it first, but it still took to much thinking and co-ordination for me for this particular purpose.
@Zabobon @_jims Thanks, I'm pleased that the topic has stimulated ideas from users with all sorts of different approaches and insights.
Now that I see how this can work I think it can be made even more seamless by using the idea of modifying the XML of a Trigger Macro by Name Action. There is a menu item to copy a Macro's UUID and a menu item to copy an Action's XML. Simply pasting in the modified XML can add a Macro's UUID to the Action's list... so, I think this will be straightforward to do and I am going to try a Proof of Concept tomorrow.
With this mechanic it should be possible to simply select a Macro from the Library and add it to a particular Trigger Macro by Name.
Okay, so here is a proof of concept. It can definitely be refined but it shows the basic concept will work.
Select any Macro in the Library and press a hotkey. It gets added into the list of Macros the 'Trigger Macro by Name' Macro is limited to. That's it.
At the moment (it is only a first proof of concept) the original 'Trigger Macro by Name' Macro is duplicated so the original has to be manually deleted. Not too bad as it is a kind of backup but would be better if the original macro was just replaced. Also I need to add in choices of hotkey, editing the list etc.
Here is video showing the proof of concept in action, adding three Macros to the list.
Okay, I have had a go at making a Macro that makes the process of adding Macros to the list simpler.
Select any Macro in the Library and press a hotkey. It gets added into the list of Macros the 'Trigger Macro by Name' Macro is limited to. That's it.
The Macro I have made stores the "list" in a Global Variable. The same Macro can be used to edit this list (i.e. to remove some or all the Macros from the list).
I'm sure it can be refined further and if I do that I will update new versions.
The Macro can be found here. (I didn't want to clutter up the current thread with versions of this idea).
I will post updates to the Macro as I refine it. First change will be ability to add multiple-selected Macros at once (at the moment it is one at a time).
Here's a tip about the Insert Action by Name prompt in the KM Editor for anyone else who may have missed it.
The idea finally occurred to me that the use of a modifier key to change this behaviour would already have been thoughtfully provided, and indeed the Wiki tells me that this is the case:
hold the Shift key down to insert the action above the selected action.
– manual:Menus [Keyboard Maestro Wiki]
