ActionScript 3 :: Converting TextArea Into TextField Component

I've a TextArea component in my MovieClip. When I double click on it, I want to switch to TextField component, allowing me to change its content. When I click outside, I want to restart its original class (TextArea).

I'm doing this, but didn't work:
element.addEventListener(MouseEvent.DOUBLE_CLICK, changeName);
private function changeName(e:MouseEvent):void{
e.target.type = TextFieldType.INPUT;
}
Where element is a TextArea (classic and dynamic text).

This is how my MovieClip looks. "Name" is the TextArea that I want to allow user changes. I'm setting it like this:
Nombre de instancia = Instance name (empty)
Texto clasico (classic text)
Texto dinamico (dynamic text)

The MovieClip is controlling my by own base class (called 'ConfLayer'). Inside it I have this:
public function doStuff(e:MouseEvent):void{
// element = TextArea 'Name'
element.addEventListener(MouseEvent.DOUBLE_CLICK, changeName);
} private function changeName(e:MouseEvent):void {
var tarea:TextArea = e.target as TextArea;
var tf:TextField = tarea.TextField; // this line throwing error
tf.type = TextFieldType.INPUT;
}

Because AS3 gives me errors, I tried this:
private function changeName(e:MouseEvent):void {
e.target.TextField.type = TextFieldType.INPUT;
}
When I double-click on TextArea element, the previous string removes and I can't write nothing.