MePlat: you should not have to fiddle with anything sight-wise on a fixed sighted revolver. I would not doubt a bit that the S&W 357s, all of them, are most likely regulated to 50 yds with fixed sights and 158 gn 'standard' 357 magnum loads but I would think this question is best answered by Smith and Wesson, not someone else.
Who knows; possibly the one or two guys who have these things can't hit beyond 10m because of age or eye condition - with all due respect to those shooters, you may not wish to take their advice. It could also be that whenever they shoot their revolvers they close their eyes or pull to the left or right - again, not the source for the most accurate information; but Smith and Wesson is, and they will tell you.
Also, if you are talking about 'shimming' a rear sight for additional elevation and or filing sight notches for a clearer picture then you really need to talk to the manufacturer.
IIRC, when I looked at pictures of those revolvers it seemed they wore Novak style sights which are not adjustable and since they are dovetailed to the frame I doubt there is any room to shim them up. Ya'll oughta call S&W and get it straight from them. jmtcw.