Martin J. Laubach wrote:
 >   One more problem: What happens if I have a subset of package foo 
 > installed, and later, when I already have three dozen of dependent
 > packages installed, find out I really need the "ext" subset too.
 > Delete everything and reinstall?

Yes. For now, please delete everything and reinstall.

Logically, pkg_add can add additional subpackages which belong
to packages already installed. But it will need more hacking on
pkg_add. I consider it a future work. If the function is really
needed, I would improve the pkg_add. I think it might be possible
without any modification on PLIST nor pkg_add user interface.

Takemura