I "deleted" 11 years of history using this[0] Chrome extension. Took a few days to get through everything, and I had to re-run it a few times because it missed things.
[0] https://chrome.google.com/webstore/detail/social-book-post-m...
[0] https://chrome.google.com/webstore/detail/social-book-post-m...
Using the "Hide" button instead of the "Delete" button I think works on untagging.