The hammers retail from S&W for $39.84, in the most recent S&W parts catalog, not counting shipping and handling.
They can be replaced by the factory, a gunsmith familiar with S&W pistols, or a certified L/E armorer.
If you know a S&W armorer, they can get the part for a slight discount, and do the work for you. If you don't, why not simply call S&W and ask how much they'd charge to switch the part and perform a general inspection while they've got it apart?
Depending on the amount of use your particular pistol has seen, it's always possible that replacing the hammer may involve replacing some other part(s), as well, depending on the condition of the existing, older parts and the "fit" of the new hammer with them ... and the pistol's functioning once the hammer's installed. A factory technician, gunsmith or L/E armorer can tell you if something like this would reasonably be required when examining your particular pistol. But like the other person said, it's commonly no big deal ...
As a certified S&W armorer, I've switched spurred for spurless, and vice-versa, for both myself and other folks ...
In my first S&W armorer's class, one of the armorer instructors told us that he switched out the spurrless hammer on his personal 3913 for a spurred hammer, because he used to be a revolver person and he simply preferred spurred hammers.
Bear in mind, though, that switching to a spurred hammer may give you the potential for a bit of "hammer bite". I can't remember, since I don't have a 4516-X at the house, but in some of the other S&W TDA pistols the grip tangs are just a bit shorter on pistols designed to be commonly equipped with the spurless hammers.
Shipping handguns isn't inexpensive nowadays ...
As long as nothing else requires repair or replacement, it generally only takes a few minutes to disassemble the pistol and replace a hammer ... but then the pistol should be both "bench tested" and fired to make sure everything is properly functioning with the new part installed.
You can call S&W at 800 331-0852, and ask to speak to someone about having some gunsmith work performed.
