Howdy
Yes and no. I am assuming you are talking about the double action trigger pull.
There are two springs that affect the double action trigger pull in any modern S&W revolver. Of course, the hammer spring will affect it. But the rebound slide spring probably has more to do with how heavy the double action trigger pull is than the hammer spring. At least, that has been my experience.
Here is a photo of a K-38 with the side plate removed. I don't own a Model 48, but the action will be basically the same as what you see here. The hammer spring is obvious. The rebound slide is the part directly behind the trigger. There is a coil spring inside it, you can see the spring peeking out of the slot at the rear of the rebound slide. Every time you pull the trigger or cock the hammer, you are compressing the rebound slide spring. When you release the trigger in Double Action fire, the rebound slide spring shoves the trigger forward again.
You can buy a lighter rebound slide spring from Wolff, but you have to remove the hammer block, hammer spring, hammer, and rebound slide before you can replace the rebound slide spring. The rebound slide is the trickiest. It is not difficult, but the spring is under a great deal of pressure. You need to compress the rebound slide spring while coaxing the rebound slide up. Brownells makes a special tool for this, but you can do it with a screw driver in a pinch. You have to be careful, because once the rebound slide spring clears the pin holding it in place, it will take off for the most remote corner of your basement, never to be seen again. If you are replacing the spring anyway, you may not care, but I don't like springs flying around the room. That's why you have to compress the spring while coaxing the Rebound Slide up. Once the Rebound Slide clears its retaining stud, you carefully relieve the compression of the spring, and you can pluck it out. Then you pop a new one in, compressing it again as you coax the Rebound Slide back into position.
Replacing the rebound slide spring with a lighter one will give you a lighter trigger pull without affecting how hard the firing pin hits a primer. You can of course change out the hammer spring too.
Here is a view of another old Smith with the Rebound Slide Spring removed from the Rebound Slide.
In this photo, I am holding the trigger back after the hammer has fallen. You can see the Rebound Slide Spring is completely compressed, trying to push the Rebound Slide forward again. There is a stud that pivots on a pin in the trigger, and when I let the trigger go, the Rebound Slide will shove that stud forward, pushing the trigger forward as it goes.
Putting in a lighter rebound slide spring will result in the trigger return not being quite as crisp, but that usually does not matter too much.
Just replacing the hammer spring will of course give you a lighter trigger pull, but not as much as replacing the rebound slide spring too.
I do not recommend the old trick of backing out the hammer spring strain screw to lighten the force of the hammer spring.