The forks compress easily without the caps on. I would advise to check both fork tubes for oil levels before removing the old springs if you're going to the trouble of doing that. I just don't trust the factory that both forks would have the same amount of oil in them. Only takes an extra minute or two to check.
IMO, if you put in the Progressive springs with the tighter windings on top, you shouldn't see an appreciable difference in the oil level. But no harm in doing a thorough job and taking the extra few minutes to measure.
Personally, I can't see changing the oil with the forks on the bike as a great way of doing it. It'll be tough to get all of the oil out of the forks since we don't have a drain plug. Might as well do it the way the book says, but that's just me.
Somebody has already mentioned strapping the bike down to the jack, but I want to re-emphasize that. It's also a good idea to make sure you don't have your jack postioned too far aft when you raise the bike. I've had the whole bike and jack tip backward on me in the past because I had the jack placed too far back. You can even place some short 2x4s, or whatever you have laying around, under the back tire to insure it won't tip backward.
