If [tag], then [tag]?

Hi all,

Was wondering if anyone knew of some way to have tags automatically added to a book if another tag is added. For instance, I might have the tag:

Subject.Wars & Conflicts.By Name.World War I

and the tag:

Subject.Wars & Conflicts.By Date.1914-1918 -- World War I

It would be nice if whenever I tag a book with "Subject.Wars & Conflicts.By Name.World War I" it automatically adds "Subject.Wars & Conflicts.By Date.1914-1918 -- World War I" as well so I don't have to do it manually.

Any ideas?