[AS3] How to apply autoSize TextFieldAutoSize on text located on Stage?

I have a movieclip, with a dynamic text inside.
This movieclip is already on stage.

I have found several solutions to this TextFieldAutoResize,
however, most of them requires to create a new text
before implementing TextFieldAutoResize.LEFT or right or center or … etc

Is there any method to apply auto resize on dynamic text which are already placed on stage?