If you were able to get the base sim installed, and all you are missing is scenery, you can simply do use the installer to add scenery at any time. If the install is missing default files, you will need to re-install or use the update option to fix that. You can always install the sim with no scenery first (it's pretty fast to do that and only needs disc 1) and add scenery later as well if install is poorly behaved.