I second this request but I think it would most likely happen for search no the tag library itself.
Changing the content of a tag in the tag library currently doesn’t apply to previously tags for that content in the library nor does it change the color when the color is changed in the library.
When I made a naming mistake with my tag, I had to preform a search on that tag and then changed the content that I really wanted which was a very manual process!
Then I went back to the tag in the tag library and change it for use in the future only.
It would be nice to have from the tag library an option to search and change all content of a tag to new content all at once. This would be incredibly helpful to change the content of tag for mass files which sometimes happens! Additionally the same option for changes the color of a tag on mass also applies.