W(h)eather the numbers actually change or not is irrelevant.
A manufacturer has a lot of options that the average mechanic does not...but a mechanic approving an aircraft for return to service must be able to verify, among other things, an accurate weight and balance. If an aircraft has been repainted and the weight or balance potentially altered, it must be weighed to make a determination of the weight and center of gravity. On a small aircraft, the weight isn't legion, but on a large aircraft, the weight change can be hundreds of pounds. Even changes in types of paint, paint thicknesses, etc, can have a significant effect.