Just automatically assign each tag with an unique ID, make it hidden from users and a new function called “synchronize tags”. When use it, the program search and compare all tags in the location and reported back mismatch tags that have same ID but different name, text color or bg color,… Then, users can choose which style they want to keep so the program can modify all mismatch tags to have that same style.
This recommendation is for sidecar method in mind, i dont know if it work with other method
or maybe a more simple approach. Disable the user ability to edit tag on file/folder, only let them move/add/remove. If they want to edit, they would have to do it in library. Then upon any changes made, when pressing ok, automatically apply these changes to all tag on file/folder. This may of course, take some times between changes, but i do believe it is worth it because of the amount of post people request this similar feature. I and everyone else have been wanting these features for years…, please consider it.
Also, please looking into the bugs that searching is not working when using tagspaces in an external drive, i posted this problem on github probably 1~2 years ago and even in ver5, this still not fixed :((