As most have said, just try it. You don't need to worry about the difference in setup - just to try the 9's.
Of course, there is a difference in the perfect setup for each gauge. If you like the 9's have it adjusted for that. I think generally a guitar setup for 9's should take 10's pretty well. Better than the reverse. And if you decide that you want to permanently switch back to 10's have it adjusted for them.
Personally, I like the tone of 10's better than 9's. However - 9's are certainly easier to bend (on a Paul). 10's on my Strat seem pretty soft. 10's on my LP are tougher on the fingers.
BTW - I just bought a 2009 (Gibson) LP Standard Plus. It's the first LP I have had in about 25 years. I love it. The new chambered bodies are different, but really rock (in my opinion).
I'm thinking about putting a set of 9's on it for a while...
