TextureImporter settings not applied

I've wrote AssetPostprocessor script to process imported sprites. Whole script is pretty plain

 public class ImpotrProcessor : AssetPostprocessor
 {
     private void OnPostprocessSprites(Texture2D texture, Sprite[] sprites)
     {
         if (assetPath.ToUpper().Contains("UI") || assetPath.Contains("Standard Assets")) return;
 
         var importer = assetImporter as TextureImporter;
         if (importer == null) return;
 
         if (importer.textureType != TextureImporterType.Sprite) return;
 
         importer.filterMode = FilterMode.Point;
         importer.spritePixelsPerUnit = 16;
         importer.textureFormat = TextureImporterFormat.AutomaticTruecolor;
         importer.mipmapEnabled = false;
 
         Debug.Log("Import settings applied on " + assetPath);
     }
 }

Although sprite settings looks fine in inspector, them not applied on sprite. I need to change any setting in inspector (otherwise "Apply button is not active) and hit "Apply".