You can edit a scene and preview changes to lightmaps and lighting without affecting the baked lightmaps.
To preview, do the following in a scene that uses lightmapping:
Unity creates temporary lightmaps and uses them in the Scene view. To check the temporary lightmaps, go to the Lighting window and select Baked Lightmaps.
To use the baked lightmaps without your changes, set Lighting Data to Baked.