Setting a variable in a textfield - possible?

Hey all, I have a very small AS3 question.

I want to do something like this, is it possible to set a variable in a textfield?

Pop this in a new Flash file and you’ll get an error.

var blah_txt:TextField = new TextField;
blah_txt.text = "One";

blah_txt.blah = 1;    // Is this possible, I get error 1119

How can I do this, or something similar?