Texture Swap + Animated Offset/Tiling

I am (trying) to learn javascript and have come across a challenge that boggles my simple mind. I am trying to combine this script:

 //vars for the whole sheet
 var colCount    : int =  4;
 var rowCount    : int =  4;
 
 //vars for animation
 var rowNumber   : int =  0; //Zero Indexed
 var colNumber   : int =  0; //Zero Indexed
 var totalCells  : int =  4;
 var fps  : int = 10;
 var offset  : Vector2;  //Maybe this should be a private var
 
 //Update
 function Update () { SetSpriteAnimation(colCount,rowCount,rowNumber,colNumber,totalCells,fps);  }
 
 //SetSpriteAnimation
 function SetSpriteAnimation(colCount : int,rowCount : int,rowNumber : int,colNumber : int,totalCells : int,fps : int){
 
     // Calculate index
     var index : int = Time.time * fps;
     // Repeat when exhausting all cells
     index = index % totalCells;
     
     // Size of every cell
     var size = Vector2 (1.0 / colCount, 1.0 / rowCount);
     
     // split into horizontal and vertical index
     var uIndex = index % colCount;
     var vIndex = index / colCount;
  
     // build offset
     // v coordinate is the bottom of the image in opengl so we need to invert.
     offset = Vector2 ((uIndex+colNumber) * size.x, (1.0 - size.y) - (vIndex+rowNumber) * size.y);
     
     renderer.material.SetTextureOffset ("_MainTex", offset);
     renderer.material.SetTextureScale  ("_MainTex", size);
 }

with the unity wiki's texture swap code:

 var frames : Texture2D[];
 var framesPerSecond = 10.0;
 
 function Update () {
     var index : int = Time.time * framesPerSecond;
     index = index % frames.Length;
     renderer.material.mainTexture = frames[index];
 }

And I guess my problem in understanding is, even though I watched some videos on index and modules I don't feel like I understand all the way yet and am not even sure if that is the answer to my question....

Anyways, my question is : How can I set this script up so that when the sprite sheet plays the final frame the texture is swapped to a different texture?