Please use this: http://unity3d.com/support/documentation/ScriptReference/WWW.LoadImageIntoTexture.html

For instance. in your case you could do:

var textures : Texture2D[];
var textureNames : String[] = [ "/isometric UV2.png", "/isometric UV2blocked.png" ];

function Start()
{
    StartCoroutine(DownloadTextures());
}

function DownloadTextures()
{
   textures = new Texture2D[textureNames.Length];

   for(var t=0; t<textureNames.Length; t++)
   {
       textures[t] = new Texture2D(4096, 4096, TextureFormat.DXT1, false);

       // Start a download of the given URL
       var www = new WWW("file://" + Application.dataPath + textureNames[t]);

       // wait until the download is done
       yield www;

       // assign the downloaded image to the main texture of the object
       www.LoadImageIntoTexture(textures[t]);
   }
}

Now you can just add texture string names for each texture you wish.