Not hard and, no, it doesn't have to be done by a gunsmith. The difficult problem is if the leaf-spring falls out. You then have to know how it fits back in. Other than that, it's just a matter of having a proper-sized punch and tapping the pin on the bottom out. Make sure that the gun is unloaded and decocked first, of course. Once the pin is out, the mainspring housing drops out through the bottom.
As far as changing it, there is no real reason to. No wear is experienced in this area so durability is not a concern. If you are doing it for peace of mind or to change the shape, then steel is fine, I guess.
[This message has been edited by badgerarms (edited October 09, 2000).]