Change font in aTextField

I can change the font of selected text, with
my_format.font = "Arial";
textFormat(my_format);
and so selected text takes the font "Arial".

I want to do it with non-selected text.
To choose font, and any text being input in the TextField from now on, to take the chosen font.
And the text that was input before changing font, to remain intact, as it was.
Just the way things are in a text editor.

That should change the Font for the whole text field, you wanna post FLA file or full code?

I'll have to 'cut' the appropriate part to post it here.
From Monday now.