This is a good question as you generally can't add weight plates to a weighted bar.  That being said, you can still add resistance to almost any weighted bar exercise.  The best way to do this would be by using bands (for some movements).  For example, for squats, you can add bands to the bar and stand on the other end. If you have a sturdy enough structure, you can also wrap the band around and attach the bar to do even more exercises; such as rows and pressing.