You can locate the config for the drop down in the file renaming dialog at this location:

~/.config/easytag/rename_file.mask

You will want to edit it with the EasyTag closed.  I have edited mine to only have the four formats I actually rename files:

%n – %t
%n – %a – %t
%d-%n – %t
%d-%n – %a – %t

Quite useful.  Have fun!