But my system is good enough at this point that it's pretty rare I introduce something new that has this kind of effect. Most changes are more subtle and affect the emotional connection I get with the music as much (or more) than easily identified "audiophile terms".
However, once I've listened to a new component/cable/acoustic treatment/speaker position for a while, I can start to identify aspects of the sound that are different. Once I know what to listen for, it's usually not hard to hear the differences when I switch back.
But even in cases where the differences are not easily identifiable, if I'm enjoying the music more but don't understand why, that's really all that counts. And the enjoyment part is not always the case - there are times when I'll make a change that I think should be an improvement, but after a while, I find myself wanting to turn the music off even if I can't identify what's wrong.
These are the reasons I will never make a decision to change something in my system based on an ABX test (unless of course I could switch back and forth over the course of days, but this has never been practical).