^^doesn't the car have to re-learn/map everything...is that helpful or destructive (could it improve gas mileage and re-route power better?) or could it be destructive and not learn it as well as it once was since the car is used?

nah its never a bad thing the car relearns and set the parameters just as they need to be if anything the car will run better and it will be more responsive until the car learns your driving habits

By just driving the car a few days the code will go away by it's self...just be patient.