string[] sprites = new string[]{

             "Assets/atlas/textures/t1.png",

             "Assets/atlas/textures/t2.png",

             "Assets/atlas/textures/t3.png",

         };

         string ab_atlas1 = "ab_atlas1";

         for (int i = ; i < sprites.Length; i++)

         {

             TextureImporter textureImporter1 = AssetImporter.GetAtPath (sprites [i]) as TextureImporter;

             textureImporter1.textureType = TextureImporterType.Sprite;

             textureImporter1.spritePackingTag = ab_atlas1;

             textureImporter1.spriteImportMode = SpriteImportMode.Single;

             textureImporter1.SaveAndReimport ();

         }