my car came with the GU2 G80, I want to swap out the gears to 3:23's when I change out the ring and pinion if I lay the spacers out in the order I removed them. Do I still need to have the rear end setup or should I take it to a shop and have them do the swap for me?

 

The rear still needs setup. It needs setup even if you just replaced the crush bushing and did not change the gears. The gears have different thickness and form.

Cheapest way to swap gears is to just buy the whole rear.