I thought that was the case, but I did a little research to see if you can define a locale code for your new keyboard map. I didn't find anything that said so explicitly, but there are a couple of features that suggest possibilities.
I found this manual:
http://www.angelfire.com/planet/linguisticsisfu...
On page 5 they talk about "Project Properties".
In there they talk about "Description" and "Language". The language is a drop down, so I assume/guess the list is being picked up from Windows. So for now you have to "borrow" an existing language until one is officially for this "new" (to computing) language. But I am wondering if the "Description" comes into play at all for the the locale code that is generated for this new keyboard.
Does the tool completely replace an existing default keyboard, or does it create a new locale code? ie if I base a new keyboard on en-CA, does that mean I can no longer use the default en-CA because it has been replaced, or does the tool create a new one based on that. If you can figure out the generated code, with a little luck you could use that code in PowerShelll.