I think you are asking if the bike has to be supported by a lift to replace the shocks.
It takes a lot of pressure to compress those shocks from their relaxed mode. On the other hand, if you are able to put one shorter shock on and then try to get the other longer shock off, it will be something like unhooking your garage door spring when the door is closed.
Be careful and think through what you are doing.
Do yourself a favor, use a bike lift and change then 1 at a time.
Yes. remove both and then lower bike to install the left and then right side. I'd bout be willin to buy a ticket to watch someone try to change out 1 side complete and then do the other