Could be dealt with in a single action which would require only 1 run.
I am still not sure whether simply writing the set tag data to a file is quicker than reading the file again, comparing it with new data and then write it or not.
See also this dicussion
where apparently MP3tag speeds up the process if nothing is to do.
To me it looks like the user would not have to think about how many files really get written. Still, as the files are touched, the modification date will probably be updated.