There are currently 4 questions with the tag harvard-referencing. Our other major bibliography style tags (apa-style, chicago-style, mla-style) all have the form
<name>-style. It would seem to make sense to change harvard-referencing to harvard-style.
I now merged harvard-referencing to harvard-style but without creating a, IMHO unnecessary, synonym. I don't think the first form will come back. The auto-completion will show the new form when someone enters
Such tag renaming can be done by the moderator using one of the moderation tools and does not create new revisions for the tagged questions, which is the preferable way.