Log exports I can implement. But undoing faves and votes sounds very difficult to tackle. Consider how the script should handle the situation where an image is faved on the target booru, but doesn't exist on source.
Simply unfaving every single image that could not be matched means limiting your faves to images that exists on both sites. In addition, image matching is not 100% reliable. It's possible for the sites to have images that are visually identical, but possess different file signatures. Or sometimes a match can only be found through the fallback search methods, meaning it has to be force enabled or running the risk of losing faves.
So what if the script only unfaves images that could be found on the source booru, but isn't faved/upvoted? Well, there is still the risk of data loss if a faved image on the target booru is later uploaded to the source. The script will see the image on the source booru is unfaved, and thus unfaving it on the target booru.
So unfortunately, I don't intend to implement this feature. It's just too much effort and far too error prone. If you only need to unfave/unvote images on an occasional basis, I would recommend my Booru Switcher
script as a workaround. Using it on an image page will redirect you to the same image on the other sites, where you can manually unfave the image.