The Script Equivilent of dragging a hierarchy of meshes over a preexisting prefab?

Hi Guys,

I'm having a hell of a time trying to update pre-existing prefabs during the OnPostprocessModel call. Using the EditorUtility.ReplacePrefab always overwrites the prefab completely.

         List<GameObject> affectedPrefabs = mapAvailablePrefabs(gameObject);
         if (assetPath.Contains("@") == false) {
             string path = assetPath.Replace((gameObject.name +".FBX"),((returnRace(gameObject)) + gameObject.name + ".prefab"));
             //Does .Prefab already exist at this path?
             //This is mainly to insure that at least one prefab is created if base prefab does not exist.
             if (!System.IO.File.Exists(path)){
                 Debug.Log("Creating Prefab: " + path);
                 Object prefab = PrefabUtility.CreateEmptyPrefab(path);
                 EditorUtility.ReplacePrefab(gameObject, prefab, ReplacePrefabOptions.ConnectToPrefab);
             }
             foreach(GameObject prefabPath in affectedPrefabs)
             {
                    //Updating PreFab
                 Debug.Log("Updating Prefab: " + prefabPath.name);
                 EditorUtility.ReplacePrefab(gameObject, prefabPath, ReplacePrefabOptions.ConnectToPrefab);
 
             }
         }

Thanks for you time! Nick