Thanks to otsune, I’ve discovered a few Greasemonkey plug-ins that aid in batch tagging Tumblr posts! Instructions and links here. If you plan on using this and have a custom domain, you’re going to have to add your own ‘Included Pages’ in the TumblrTagCommand settings.

I am: going through tons of old posts and adjusting tags.
I am: ready to blow my brains out.
I am: apparently a little obsessive-compulsive.

Batch edit tags. I wish so hard that I could do this.

david:

Can you do me a solid and tag your blog in the Directory to test the new tagging changes?

It’s still a bit clunky.  New tags won’t show up immediately in the All Tags list, but should appear in the autocomplete list when entering your tags.  NSFW blogs aren’t included yet.