RegEx to remove Square Brackets

Action "Format value" ... or ... Convert "Tag-Tag" Tag-Field: _FILENAME Formatstring: $regexp(%_filename%,'\s*\[.+\]$',)

from:
Niney The Observer - Blood And Fire [12 Version]
to:
Niney The Observer - Blood And Fire

Action "Format value" ... or ... Convert "Tag-Tag" Tag-Field: _FILENAME Formatstring: $regexp(%_filename%,'\[(.+)\]','$1') From: Niney The Observer - Blood And Fire [12 Version].mp3 To: Niney The Observer - Blood And Fire 12 Version.mp3

DD.20150613.1121.CEST

To make sure to see only files having a filename with opening and closing square brackets, then for example set the Mp3tag Filter to ...
"%_FILENAME%" HAS "[" AND "%_FILENAME%" HAS "]"

... or ...

To make sure to see only files having a filename with a square bracket clamp at end of the filename, then for example set the Mp3tag Filter to ...
"$regexp(%_filename%,'^.+?[.+?]$',)" IS ""

DD.20150614.1840.CEST