Over time, users like myself may have accumulated a large collection of Format Strings, which to employ when using the tags to format file names. Some of these Format Strings may become redundant or defunct, and that inflates the list of format strings to unwanted proportions, making it difficult for the user to spot the appropriate format string. These can be removed the usual way, but at the moment the user can only remove either a single Format String or the complete history. Would it not be useful to add the option to delete any selection of format strings from the Format String history to avoid deleting them all at once, which forces a complete rebuild?
The history is stored in the file mp3tag.cfg.
This file cannot be edited in a simple way.
If you delete it, you reset MP3tag to more or less the initial install status (exceptions are probably the columns, genres, actions and exports which are kept in separate files).