There isn't currently a way to prevent these commands from being recorded in the History List. The blank/un-blank entries can simply be deleted. Layer visibility can mean dependencies and so requires more caution - a lot of people use layers because it is a system they "grew up" with using the earlier generation CAD systems. With VX's multiple-Objects-one-file approach, and sub-part history Objects, layers should rarely be required. The main use for layers in a 3D model is the support of a layer management structure imported with the geometry of an external file (e.g. IGES).