As there is a search option already on this page would it be possible to implement an " if found replace with box" to allow a user to type in a whole or part of a tag search but then implement the change. Hence if a tag requires to be changed on mass then it would save a lot of typing.
Perhaps have a global "replace all option" as well as a safer method of skipping through one at a time so if you have over looked something then you have an option to skip this incidence & skip to the next find.

cheers Ian