There are a few ways to make objects persistent. One way is by loading the data each time, and then pulling specific data to change the object into the way it should be by storing that data in a
system area. An example would be making a cube, and then getting the data to set the size, color, position, rotation, and other things from the system area. When making such an area, after setting up the area and data, the world needs to sleep (reset), them upon waking it will be persistent. Using this way, you can also add a script call to set it.
Another way is making the object in max or maya and then adding that object to the edit instance of that area.