If you are just talking the cradle you can swap the whole thing just support the front of the engine if you have a stock air box so you dont rip the boot.
I did one valve cover in chassis. I took about twice as long as pulling the engine which is a 30 minute job if motivated and you dont have nerf bars. If you still have the locating dowel in the valve cover it is very difficult to remove the valve cover. The other issue is getting all the seals lined up and leak free. Its just nowhere worth it to try to do in chassis.