Manual Template Creation in Master Style?
 

I need to create a custom template in the Master Style, in order to avoid creating and maintaining a separate copy for each of my (20) styles. It appears that one cannot directly edit or create templates within the Master Style. Am I missing something, or is this simply not possible?

You need to turn on debug mode in order to add a template to the Master Style. Add this to your config.php file:

Or just create 1 (non user selectable) style in which you make all your template edits, and set all your other styles as child of this parent style.