You can do that, but I'm pretty sure that the rotor will prevent access to the underside of the ball joint where it sits in the "cup" of the spindle. I'm almost certain that for the same reason there is not enough room to use a screw type ball joint installation press tool and I'm pretty sure it will be impossible to get the spindle with the hub and rotor still attached positioned in an H-frame type press to remove or install the ball joint. So you can take the spindle off with the hub and rotor attached but you wouldn't be able to accomplish much concerning the lower ball joint once you did.