Always create own theme? HTML reverted when updating 2.7 to 2.7.x

So I had made a blog for my friend’s site which I skinned using the default Kubrick theme. I pointed the CSS path to his regular CSS sheet rather than use the styles.css sheet in the default folder. I never renamed the theme in the styles.css to my own, never made new theme folder, and made many structural HTML edits to templates like index.php, archive.php, sidebar.php, etc.

When I updated to 2.7.x from regular 2.7 by clicking the “Update to…” link in the WordPress dashboard, the templates all reverted back to the native Kubrick HTML markup and the stylesheet once again pointed to the relative theme’s css path.

So my big questions are:

• If I’m editing the Kubrick theme at all, should I always create my own theme/directory? Would this prevent my new theme’s HTML from reverting back to native Kubrick HTML?
• Does updating via the dashboard like this always revert back to Kubrick’s native template HTML?

THANKS