I landed a commit last night that allows tags to be renamed across a blog. When you do so, all pages affected by those changes are automatically queued for republishing.
One tiny drawback of implementing this right now: There's still no mechanism for locking pages for editing. It's possible renaming a tag while a page is being edited could have weird side effects.
To offset that, I added a little safeguard. if you attempt to edit a tag used by a page that has itself been modified (or even just opened) in the past hour, you'll get a warning. It's not a perfect solution but it's a nod in the right direction.