Как изменить какие либо данные в существующей строке JSON?

[mihael_p]

В файле храню вот такую строку JSON :

{"personajes":[{"npc1":[{"lastLevel":6},{"cNum":["2","3","2","0","3","0","0","2","2","0"]}]},{"npc2":[{"lastLevel":1},{"cNum":["4","3","2","0","3","0","0","0","0","0"]}]},{"npc3":[{"lastLevel":5},{"cNum":["2","1","2","0","3","0","1","1","0","0"]}]},{"npc4":[{"lastLevel":8},{"cNum":["2","3","2","0","3","0","0","2","0","0"]}]},{"npc5":[{"lastLevel":9},{"cNum":["2","3","0","0","3","0","0","0","1","0"]}]},{"npc6":[{"lastLevel":3},{"cNum":["2","3","2","1","3","1","0","0","0","0"]}]},{"npc7":[{"lastLevel":5},{"cNum":["2","3","2","0","3","0","2","0","0","2"]}]},{"npc8":[{"lastLevel":4},{"cNum":["0","3","0","0","3","0","0","0","0","0"]}]}]}

Как изменить, допустим вот этот объект:

{"npc5":[{"lastLevel":9},{"cNum":["2","3","0","0","3","0","0","9","1","0"]}]}

Возможно ли такое сделать, или же нужно записывать всю строку целиком?
Пишу на AIR. Пытаюсь сделать это с помощью

FileStream FileMode.UPDATE

Вот код:

                        var prefsFile:File = File.documentsDirectory;
			prefsFile = prefsFile.resolvePath("preferences.txt");
 
			var info:Object = {"npc5":[{"lastLevel":9},{"cNum":["2","3","0","0","3","0","0","9","1","0"]}]};
			var ss = JSON.encode(info);
			var fs:FileStream = new FileStream();
			fs.open(prefsFile, FileMode.UPDATE);
			fs.writeUTFBytes(ss);
			fs.close();

[DaFive]

Можно конечно высчитать позиции символов и от них перезаписать нужное количество. А можно и грохнуть всю строку в файле и записать новую.