Make a clone of the existing route, give it the new name and then delete the baseboards from it that you don't want. Save regularly as I've had the program lock up when I've deleted a lot of baseboards at one time.
You will have to do the same thing with each layout that you want to use sections from and then merge them into the main route when you need them. It's a long boring job but I don't think there is any other way to do it. It may be quicker to build each section from scratch when you need them.