Need a way to rotate a chandelier *without* rotating its mounting point
You probably can use a universal mounting plate (sometimes called a crossbar)



These come in various configurations. 



You can usually thread bolts downward and hold them in place with nuts. These will be used to hold the chandelier. Then mount the plate to the box, rotate to adjust the angle you want. Then mount the fixture to the plate.

This works with fixtures up to a moderate weight. It should not be used with very heavy fixtures and definitely not with a fan.