Change scale in lightmap (Prefab property) by script

Hi,

I do a script which change the scale in lightmap by script with this function :

 private void ScaleInLightmapAll (GameObject go)
     {
         //Check if he got a renderer
         if (go.renderer != null) {
             //Serialized my object to allow to modify every property in it
             SerializedObject so = new SerializedObject (go.GetComponent<Renderer> ());
 
 //            Debug.Log ("Scale value : " + so.FindProperty ("m_ScaleInLightmap").floatValue.ToString ());
 
             //Find the property and modify them
             so.FindProperty ("m_ScaleInLightmap").floatValue = m_nScaleInLightmap;
 
 //            Debug.Log ("Scale value after : " + so.FindProperty ("m_ScaleInLightmap").floatValue);
 
             //Apply the modified properties
             Debug.Log ("succes ?   " + so.ApplyModifiedProperties ()); //Send true but this is working ? oO
 
 //            Debug.Log ("Scale value after : " + so.FindProperty ("m_ScaleInLightmap").floatValue);
         }
     }

All my debug line seems ok before and after but when I bake my lightmap with another script, my lightmap is bake with the initial value of each prefab (1).

Someone got an idea on this, it can be a good thing ;)