Trouble with an editor script replacing materials

Hmm something seems wrong with unity awsers (missing post button under ask a question)
So lets try here.

In the code below I search for a material with a specific name in my selection and replace it with supplied material.
My debug log reports a changed material name but in my view nothing happens and the object still has the same material.

Any clue whats wrong with my script?

Code (csharp):

1. public class SwitchMaterialsTest extends ScriptableWizard
2. {
3.     var replaceMaterialName     :String;
4.     var newMaterial             :Material;
5.  
6.  
7.     new function OnGUI() :void
8.     {
9.         var allowSceneObjects : boolean = !EditorUtility.IsPersistent (this);
10.        
11.         replaceMaterialName = EditorGUILayout.TextField("replace material name: ", replaceMaterialName);
12.         newMaterial = EditorGUILayout.ObjectField("new material:", newMaterial, Material, allowSceneObjects);
13.  
14.         if(GUILayout.Button("Replace"))
15.         {
16.             Replace();
17.         }
18.     }
19.  
20.     @MenuItem("test/Switch Materials test")
21.     static function Init() :void
22.     {
23.         var window :SwitchMaterialsTest = EditorWindow.GetWindow(SwitchMaterialsTest, false, "Material Switcher");
24.     }
25.    
26.    
27.    
28.     function Replace() :void
29.     {
30.         for (var item :GameObject  in Selection.gameObjects)
31.         {
32.             // Grab all renderers in gameobjects and childs
33.             var rRenderers = item.GetComponentsInChildren(Renderer);
34.            
35.             for (var rRenderer :Renderer in rRenderers)
36.             {
37.                 var materials = rRenderer.sharedMaterials;
38.  
39.                 for(var mat :Material in materials)
40.                 {
41.                     if(mat.name == replaceMaterialName)
42.                     {
43.                         mat = newMaterial;
44.                         Debug.Log(mat.name);
45.                     }
46.                  }
47.              }
48.          } 
49.     }
50. }