ActionScript 3.0 :: Create An Unsealed Textfield?

I am trying to create an unsealed textfield, so I can dynamically create properties on it. I have this class which is the dynamic text field:

Code:
package {
import flash.text.TextField;
public dynamic class DynamicTextField extends TextField {
public function DynamicTextField() {

[code]...

but I am trying to write a function that replaces an already made textfield with this one.Here is the function which does that:

Code:
function makeDynamic(field:TextField) {
var newText:DynamicTextField = new DynamicTextField();
var xml:XML = describeType(field);

[code]...

This works well, it replaces the textfield with a dynamic one, but if the textfield has a variable name such as:

Code:
var field:TextField = new TextField();

then the new dynamictextfield won't have the name 'field'.