The only time you make any changes is when your on a training ride!!! When I decide to make minor changes, I always mark my old position, make the change and go for a few rides. I bring the appropriate tools along to make additional changes as needed during the ride. I evaluate my changes to determine if they were beneficial or not.
Note: These minor changes are only made after I've gotten a professional bike fitting.Well worth it! It makes no sense spending big $$$$ on a road bike and than just winging it when it comes to bike fit.