Using assembly items

Does anyone know if an item can be setup as an assembly with variable members? We have a package of stock items sold as a group. We will sometimes change a component of the group as stock levels change. For instance, we sell golf discs (frisbees used to play a sport like golf). They come in various models, but are essentially the same value. Usually the assembly would consist of 3 certain models, but occasionally we may be low or out of a model, another model would be substituted for it. We are currently using kits for our package, but