How can I export the Extended Tags (Alt+T) info ?

Yes. See Example:

UNSYNCEDLYRICS:'eng||I search for phrasesU+000DU+000ATo sing your praisesU+000DU+000ABut there aren't any magic adjectivesU+000DU+000ATo tell you all you areU+000DU+000AU+000DU+000AYou're just too marvelousU+000DU+000AToo marvelous for wordsU+000DU+000ALike glorious, glamorousU+000DU+000AAnd that old standby amorousU+000DU+000AIt's all too wonderfulU+000DU+000AI'll never find the wordsU+000DU+000AThat say enough, tell enoughU+000DU+000AI mean they just aren't swell enoughU+000DU+000AU+000DU+000AYou're much too muchU+000DU+000AAnd just to very, very --U+000DU+000ATo ever beU+000DU+000AIn Webster's dictionaryU+000DU+000AAnd so I'm borrowingU+000DU+000AA love song from the birdsU+000DU+000ATo tell you that you're marvelousU+000DU+000AToo marvelous for words'

Each Sequence of "U+000DU+000A" stands for a CR-LF-sequence.
After importing the contents into a tagfield you have to replace the "U+...." placeholder sequences with CR-LF-sequences, e. g. using an action Tagfield Format ...

$replace(%tagfield%,U+000DU+000A,$char(13)$char(10))

... to make the linebreaks within this tagfield visible to the user.

DD.20080401.1538.CEST