I am starting to think that "what you mean by a sub theme" is not what we are helping you with. We are advising on creating a subset/variation of an existing theme.

I think that you simply wish to create certain changes to a base theme by creating a folder containing those changes and nothing more. As an example, say for instance that one of your requirements was to change part of the css or maybe one line of the page.tpl.php of a base theme. You, ideally, just want to have those bits of code in a file and have it read by the base theme.

You wish your changes to be displayed as a choice in the [Appearance] list. You cannot do this! The [Appearance] system reads a pre defined structure. To do what you want means redefining that structure in core and due to the inherrent dangers, no one with any appreciation for the developers would contemplate such unless there were a distinct community need.

A theme is a theme is a theme. It may be a subset but is still a variation of a theme reqiring certain components which are acted upon by the core system.

May I suggest that you study the Zen system of theme/subtheme. It can give you an underlying tone of how and why.

On thinking more deeply about this, I can see merit in such a proposal as Drupal would need only 2 themes, Admin and say Bartik. One could possibly over ride tiny parts of the base theme to create an entirely new look and feel.

Such things are possible in Ruby on Rails if one wanted to learn.

Roger

No. I haven't done that for a very specific reason and that reason is that your recommended procedure does not give me a sub-theme; it gives me a custom theme which is a modified copy of