I have an `04, so I have the preload thing whipped going in.
You have to take the fork off, and take the top off, for a fork oil change, correct? If so, then 90% of the work is already done. At that point, we may as well change springs. I hear they're not too expensive.
I had my 929 re-done front and rear, and yes the transformation is amazing. I already have an Ohlins on the rear of the 919. Got lucky, bought mine used. Best $$$ I have spent on the 919.