Only PostProcess/PreProcess on new assets

For those who run across this in the future, the following answer really helped me out. The key is to do a check to see if there's an asset currently at the assetPath of the new asset. If not, then you can do you're processing:

http://answers.unity3d.com/answers/468255/view.html

Here's the OnPreprocessTexture function I'm running:

 void OnPreprocessTexture () {
 
     //Get the TextureImporter 
     TextureImporter import = assetImporter as TextureImporter;
 
 
     Object asset = AssetDatabase.LoadAssetAtPath(import.assetPath, typeof(Texture2D));
 
     if (!asset) {
         Debug.Log("NEW");
         
         //Set it to a Sprite
         import.textureType = TextureImporterType.Sprite;
 
         //Set to 1 pixel per unit
         import.spritePixelsPerUnit = 1;
 
         //etc.
 
     }
     else {
         Debug.Log("OLD");
     }
 }