I think you are right. Mp3tag doesn't remove folders. But it can merge two (or more) folders into one folder, thus acctually reduce the number of folders.
But when I can't rename that folder (ex parent folder) in the same action group.
However, I can reach my goal, if I split it into two action groups:
Begin Action Group &Ordner Umbenennen#Überordner weglassen (step &1)Action #1
Actiontype 5: Format value
Field ______: FOLDERNAME TEMP
Formatstring: %_directory%
Action #2
Actiontype 5: Format value
Field ______: _DIRECTORY
Formatstring: .</b>
End Action Group &Ordner Umbenennen#Überordner weglassen (step &1) (2 Actions)
Begin Action Group &Ordner Umbenennen#Überordner weglassen (step &2)Action #1
Actiontype 5: Format value
Field ______: _DIRECTORY
Formatstring: %FOLDERNAME TEMP%
Action #2
Actiontype 9: Remove fields
Fields to remove (semicolon separated): FOLDERNAME TEMP
End Action Group &Ordner Umbenennen#Überordner weglassen (step &2) (2 Actions)
My goal was to reach that with one action group and without temporary tag fields. But I think it's not possible