Is the question here about loading a route onto an Edge device, or about changing the base map?
Loading a route is straightforward and supported by any of the Edge devices for the last ten years or so.
You export a .fit file from rwgps or whoever and copy it into the New Files folder on the Garmin device. Or else link the RideWithGps accounts with Garmin account and you just favorite the route on rwgps and over it goes.