Does removing spacers require a refit? As I get more and more used to my bike's aggressive geometry, I'd like to slowly remove the spacers. I have two right now and my LBS who did the fitting said you can remove them as you get more used to riding aggressively. 

If I were to remove these spacers in the future, do you need to readjust any other parts of the bike to maintain a 'good fit'? Or will compensating elsewhere simply negate the effect the removed spacer will have (in terms of getting more aggressive/aero)?

Can I simply remove a spacer and be done with it? Or should I get a refit while removing a spacer?
No need for a refit, but I would have the bike shop do the work if they'll do it for free.  Normally the washer is just moved from under the stem to the top so no cutting of the fork steerer tube is required.