[iCluster]

Я бы сделал так:

package  
{
    import flash.display.Sprite;
    import flash.events.MouseEvent;
    import flash.text.TextField;
 
    /**
     * @author Roman
     */
    public class TestButton extends Sprite 
    {
        private var _button: MyButton = null;
        private var _textField: TextField = null;
 
        public function TestButton()
        {
            _textField = new TextField();
            addChild(_textField);
            _textField.text = 'someText';
 
            _button = new MyButton();
            addChild(_button);
            _button.addEventListener(MouseEvent.CLICK, onButtonClick);
        }
 
        private function onButtonClick(event: MouseEvent):void
        {
            _textField.text = 'otherText';
        }
    }
}