Nope, it is not possible to change the oil with the shock in the frame. Take a look at the shock service post and let us know if you have any questions.
As for oil weight, I just serviced my shock and used 10 weight Bell Ray Suspension fluid. You CAN NOT use fork oil in the shock, no matter what the guy at the motorcycle shop tells you. Use the right fluid and you will be a happy guy. Use the wrong fluid, and your shock will fade after the first 1/2 mile as the oil foams from the heat. Your shock then becomes a pogo stick. Better have a good helmet...
Rick