IW3xRadiant can create a prefab from selected objects.
It can also stamp prefabs back into its single components.
Convert Selection to Prefab
- Select everything you want to include in your prefab
- Use the context menu and hit Convert Selection to Prefab (or Menubar > Selection)
Stamping Prefab
- Select the prefab
- Use the context menu and hit Stamp Prefab (or Menubar > Selection)