That mechanism was far from obvious. I did enter a name; apparently that text only appears in the URL, not the page.
I also changed the background color, and that was apparently lost when I went back to adjust from 'single site' (which was not confining searches to news.ycombinator.com) to 'multiple sites'.
I see what you're trying to do with the direct click-to-change customization, but the modality/light-boxes/workflow is very confusing and frustrating. I would suggest being unapologetically web-form-like: every change should require a 'submit' to take effect; result in a full-page-reload; the reload should show the change (no separate 'preview' mode).
