Event.currentTarget.visible = false back to true

Hi, I've got a tricky issue, I' m making a game involving learning activities. In this one, I've got to push letters on a screen and compose a word. Each time you click on a letter it sets its state to false, so you can't click it again. Everything as worked so far, but right now I don't know how to set back to visible the letters I clicked on.

Basically I've to do this, for instance, if you make a mistake selecting the letters you want for composing the word. I managed to create a delete button you can press, so the letter will be pop out from the textField, but how can I set the button/letter back to visible ?

I tried to push the clickedLetters into an Array, but then they become Strings so visible = true won't work. Any help ?

Thanks

private function takeTheLetter(Event:MouseEvent):void
        {
            var letterTraced:String = Event.currentTarget.letter.text.charAt(0);
            clickedLettersArray.push(letterTraced);
            //show the letters that are typed;
            var composeWord:String = clickedLettersArray.toString();
            composeWord = composeWord.split(",").join("");
            hero_txt.text = composeWord;
            //remove the pressed letter
            Event.currentTarget.visible = false;
            currentTargetArray.push(letterTraced);
            trace(currentTargetArray);
        }
private function deleteTheLetter(Event:MouseEvent):void
        {
            clickedLettersArray.pop();
            //set the array back to a string;
            var correctedWord:String = clickedLettersArray.join(",");
            //set the true sprite to compare
            correctedWord = correctedWord.split(",").join("");
            hero_txt.text = correctedWord;
        }