Sld, the laws here are not like that. For a gun to be "on the state's list" the manufacturer must submit it for evaluation. Any variation requires a new submission by the manufacturer. I.e. a nickel finish instead of blue, 4" instead of 6" barrel, etc.
However, once legally in the state, the owner can modify it without a problem. Change barrels, get a new cylinder, etc. Anything, except something like an auto-sear, or hi-cap mag.
My question; can I change slides to a different length, or does the XD-S have some weirdness that would cause a functioning problem?