After mild frustration with the difficulty to make top-level "plain old folders" within Eclipse for visual-organization purposes, I discovered that the thing I'm after is called a "working set". Hooray! But they don't seem to be rename-able, by any of the apparent avenues (right-clicking on it or using the Configure Working Sets window).
Is that just the way things are, since no one should be so lazy as to refuse making a new working set with the right name and transferring everything over? Or am I missing something obvious?
I also have a more minor question whose answer I already think I know. Can I tell a specific working set not to change its icon to have the "red X" when one of its children has an error? Nothing in the preferences under Debugging suggests to me the ability to turn off the automatic icon-changing. It's a useful feature, but I have a few simple practice projects with very basic errors, and I don't need the visual reminder to "fix" them, especially if they're in my "Practice" working set, whose icon I'd prefer not to change.