Nope, not currently. We can create custom mapsets for fleet usage though.
The maps in Overland Navigator have all been reprojected into a common map projection so that they can be tiled together as one giant seamless map. They've also been compressed so they take up less than 1/5th the space of off the shelf USGS maps, and indexed with a high performance spatial index so they can be retrieved as fast as possible.
From a user pespective this improves performance, and makes it so you never have to select which map to load when you reach the edge of a map. It just looks like one giant seamless map. It also means that it automatically switches between different map series depending on how zoomed in or out you are. The goal being to keep the software as simple as possible to use by just doing what you'd naturally want to do anyway.
Craig