this might help you on your way
add 2 new fonts to your Library with linkahe identifiers - f1 and f2
add code to main timeline to create textfield inside a movieclip
use onEnterFrame to animate (and change)
this is purely an example and should be modified to suit your project
Code:
fm1 = new TextFormat();
fm1.size = 32;
fm1.font = "f1";
fm2 = new TextFormat();
fm2.size = 22;
fm2.font = "f2";
this.createEmptyMovieClip("holder",100);
holder._x = holder._y = 50;
ref = holder.createTextField("txt",101,0,0,100,35);
ref.type = "input";
ref.autoSize = true;
ref.border = true;
ref.embedFonts = true;
ref.borderColor = 0xFF0000;
ref.textColor = 0x0000FF;
ref.text = "F1 FONT";
ref.setTextFormat(fm1);
this.onEnterFrame = function(){
ref._x += 1;
ref._x > 30 ? func1() : null;
ref._x > 60 ? func2() : null;
ref._x >100 ? this.onEnterFrame = null : null;
}
function func1(){
ref.autoSize = true;
ref.borderColor = 0x00FF00;
ref.textColor = 0xFF0000;
ref.text = "CHANGE TO F2 FONT";
ref.setTextFormat(fm2);
};
function func2(){
ref.autoSize = true;
ref.borderColor = 0xFF0000;
ref.textColor = 0x0000FF;
ref.text = "ORIGINAL FONT";
ref.setTextFormat(fm1);
};
hth