Modifying and Saving a GUITexture

I've got a series of buttons in my game and I want to dynamically create 'over' states for the buttons. What I would like to do is take my 'normal image', adjust the alpha and save it as a different texture so I can use them both independently.

I have a script called 'InterfaceButton' which accepts normalTexture:Texture2D and overTexture:Texture2D as arguments.

I want to add this script to a dynamically created button:

     for(var i=0;i<componentsSelection.length;i++){
  var instrument:GameObject = new GameObject();
  var normalTexture:GUITexture = Resources.Load(componentSelectedIcons[i]);
  
  instrument.AddComponent(GUITexture);
  instrument.transform.position.z = 5;
  instrument.transform.localScale = Vector3.zero;
       
  instrument.guiTexture.texture = normalTexture;
  instrument.guiTexture.pixelInset.x=Rect(x,y,width,height);
  x += (width+rightPadding);
  
  var buttonScript:InterfaceButton = instrument.AddComponent(InterfaceButton);
  buttonScript.normalTexture = normalTexture;
  buttonScript.overTexture = //how to manage this?
  }