First: e621 AJAX Fix
If you're privileged or better, you might have noticed that when you update a lot of posts at once (using the built-in tag script utility), some posts aren't properly updated. This is caused by the server going nuts when many concurrent requests are made at once.

This scripts uses a single connection, and in case of failure, if the server was busy, waits ten seconds and retries.

To install it, go to Source code, copy the code and paste it manually into a file called "whatever.user.js". For some reason the file download is an old version which doesn't work properly.

Second: AFTagger
I made this one to tag the massive amount of posts without either "feral" or "anthro". It adds a select box on each post, when you can select "Anthro" (by default), "Feral" or "None". Once you've updated them all, click on the "Send post types" on the left column, and just wait.

For this to work you need being privileged, and I'll also recommend using the first script.

This one hasn't been updated and can be installed by just clicking on the "install" button.

very nice, will give them a try

I'm bumping this to ask e621 programmer a question: could it possible to modify https://e621.net/post/update.json so that it accepts an array of posts rather than a single post?

Using that modification and a slighty modified version of the first script would make possible tagging an entire page using a single query. This means less time for the tagger, and less overhead for the server.

The above links are dead, but these scripts are still available here:
e621 AJAX Fix
AFTagger

Any privileged+ know or care to check if they still work?