Jeff Bartels of Autodesk explores some of the benefits of using the Civil 3D Toolspace Prospector tab to work with and manage Assemblies.
From the Jeff Bartels YouTube Channel.
and the Civil Immersion blog.
Right Click is your Friend in Civil 3D.
Your initial take away should be that you can somewhat protect your current Assembly collection by removing them from Modelspace.
You should recognize that Civil 3D considers Assemblies, Subassemblies, and PKTs as Data in the Civil 3D object model not as a Style. In other words, Assemblies are more like Point Groups (a display collector) than Points (the collected data). Needless to say - there are referenced Styles attached to Assemblies.
The current glaring lack of even basic Import and Export tools for Assembly collections in Civil 3D is more than annoying.
The work-arounds are basic AutoCAD command Insert/Explode and WBLOCK methods which create some maintenance hassles that can be easy to miss.