The halacha-jewish-law tag is the most populated by far. It covers more than 400 of the questions, and could probably apply to at least another 400. It seems to me that in its current incarnation, it's so broad that it would never pass the "would anyone want to browse it?" standard I proposed here. On the other hand, it is potentially useful as a way to divide the site broadly into Halachic and Aggadic types of questions.
Leave it alone.
Try to add it to all Halachic questions, past and present.
Redefine it as only for questions about Halacha (e.g. history of, philosophy of, rules of, etc.) rather than of Halacha (e.g. Hilchot Shabbat, Hilchot Kashrut, etc.) and strip it from all specimens of the latter, past and present.
Redefine it only for future questions.