Deontologist, having read your two posts above I am having trouble understanding what you are seeing. You shouldn't have to "rewire" for a stem change on a typical threadless setup. I wonder if you either have a single piece handlebar/stem or if you are calling the steerer tube a stem. I only say this because you say you are new to bikes.

Perhaps you can look at one or both of these videos to understand how the stem can be removed and flipped or replaced without replacing the handlebars:

How To Change Your Threadless Bike Stem - Performance Bike Learning Center

How To Change A Stem - Bicycle Mechanics | Global Cycling Network