DrO,
Would not just adding a preference to use a custom image file name, that overrides what is currently done, be simpler to code than the enable/disable for each naming preference shown in your screenshot?
The naming rules currently used could be listed and would be the default.
If the <Alt+3> tag editor is used, to put an external image file in the folder of the song file being edited, it will rename the image file to what's in the song's %album% tag if one exists or "cover". I assume this behavior will not change.