Is it a sin to make a gun more versatile? Not in my book. How much does an alteration lower value depends on what is done to the gun. Good rule of thumb might be to evaluate the gun. Is it a rare gun or rare combo of features, high condition or mint, unfired, NIB or some other unique reason that this gun above all others has special value? A model 37, while nice, mostly likely does not have enough special reasons to be so unique that alterations will vastly destroy value or function unless it is about top few percent in condition or a rare version. One of the million plain field guns certainly is a candidate for alterations.
If not, alter as needed but use some amount of respect of what ought to be done. No proporting barrels, no adjustable combs or morgan pads, no chrome plating or high polishing of all the case colors, no slathering trueoil on like a prostitute at a MaryKay convention, no adding vent ribs to a double, no decals added to stocks or barrels, no glow worm beads or sights and no camo paint or tape for anything nicer than a Nitro Special and not even then if a high condition gun.
