Factory main and rebound springs are balanced against each other, so changing just one or the other may, or may not cause problems.
At Smith & Wesson they cannot individually tune each revolver they make. Therefore the springs are designed to insure
reliability, no matter what. They have no way to know what particular ammunition or brand of primers you may use, or if your revolver will develop cylinder end-shake or some other condition that may affect primer ignition, or if the internals ever see a drop of lubricant.
Both the manufacturer's and
professional action jobs have far more to do with the fitting of various lockwork parts and the cylinder assembly (yes! the cylinder assembly is important) then simply switching out springs.
No matter how you cut it, switching springs will reduce
absolute reliability. How important that reliability is depends on what you plan to use the revolver for. But if the intended use includes personal defense I suggest that you return the gun to Smith & Wesson, or send it to a professonal gunsmith with a reputation, and have them do a complete
street action tune-up.
Incidentally, while they won't come out and say so, the company is delighted when individuals "polish" parts or change springs. Should the revolver fail at a critical time it is unlikely they can be sucessfully sued.