There seems to be no way to mark a group of files and then delete a keyword from all of them without changing any other keywords that may be present and that may differ among the selected group. That operation makes it easy to change keywords in old files. This works very smoothly in the standalone version of picasa, which has not been supported for some twenty years.You can select files with irfanview and then use the irfanview filelist wth exiftool, but that is much more tedious.
