Two Question on Altering File Content

Hi all :D,
I wanted to know how to change a node value of an .xml file using actionscript. Thats my first question.

My second Question: how can I write to a text file using AS 3.0?

Thanks

Q

Here is an example. use replace().
var myXML:XML=new XML("<text><item>item 1</item></text>");
myXML.replace(0,<item>item 2</item>);
trace(myXML.item);