I have ended up with inconsistencies across my FLAC Tags. For example, works by Mozart have Mozart, W A Mozart, Mozart W.A. as the album composer. Is there any way I can batch edit multiple folders to change that field/tag on all tracks/files to, say, Mozart W A?
You can load more than one folder at a time into MP3tag (either open the root folder or select and d&d the folders from the Windows Explorer into MP3tag).
After loading you can apply a filter, e.g.
%artist% HAS Mozart
Then select all the files.
Enter the favourite name into the corresponding field in the tag panel
Save the modification
Or what do you mean by "batch"?
Assuming that by 'batch' you simply mean editing a whole selection of files at one go, there is one other tweak you can use in the procedure described by ohrenkino.
If one of the values for (in your case) Composer is actually the one you want to use for all files, you will find that, when you select multiple files, you will have a available in the Composer field a drop-down list of all the values of that field in the selected files, plus and . Selecting your preferred value and saving will apply that value to the whole selection.