The main issue is that when you pess out the hub, there is no way to support the inner race(s) because the hub flange is covering that area. Therefore, you'll have to press directly on the hub, and it usually takes the inner race with it, and if not, it puts high amounts of axial loading which usually ruins the bearing anyway.
To be honest, I don't remember exactly how the rear hubs are assembled (it's been awhile). I suppose if you pressed on the outer diameter of the bearing, and then use a bearing cup to get in between the bearing and hub, properly supporting the inner race and pressing out the hub, you could do it without damage. Most people don't have access to a press or the correct tools, so this isn't an option for most. Luckly, I have both and I could give it a try, but I would highly recommend replacing the bearings when you do the hubs, as they may get messed up, and they prob. have 150k on them anyways....
::EDIT:: I just found a picture of the assembly. I can't see a way to press them apart without wrecking them.....autozone near my apartment has them in stock for $32 each, or I can pick them up in NH and save on taxes.