Yes, they are a press fit. It can be done on the car. After clearing the strut from the ball joint, support the bottom of the control arm with an axle stand, and smash the ball joint out with your BFH, then place the ball joint in position from the bottom and support the ball joint with the axle stand, having a short piece of exhaust tube or similar to sit the ball joint on helps. Then tap the control arm down, forcing the ball joint up into position. Hit the control arm in alternating strikes on opposite sides of the ball joint to make it go in evenly.
Or you could just use a press and press the old one out and the new one in. This requires total removal of the control arm of course.