Hi Zuiko
There should be plenty of room to do it with the tire on. I debated about that myself, but the JD mechanic recommended it, and it wasn't that big a deal for me. I don't have any wheel weights, although it is still a heavy assembly.
You may lose a little more fluid since you will have to put the plug in from a sideways angle, but it shouldn't be significant. I would pull the pin that holds the brake rod, and lower it out of the way.
As far as removing the wheel, just jack up the rear axle until the wheel slides off the hub, and then just roll it back and rest it against the ballast box, or other handy implement. Do the reverse to mount it back up. There is no need to lift the wheel and tire, just some gentle wrestling...
Please remember to put a jack stand under the axle at all times for safety !!! I had a friend crushed and killed when a jack slipped and he was working alone many years ago...Ouch
Good Luck and Have Fun,
John