I think this concern takes the "don't use a custom gun for SD" mantra quite a bit too far.
As Dr. Meyer (GEM) and others have pointed out, some gun modifications could potentially be used to sway the, otherwise ignorant, jury that you had some excessively aggressive attitudes or tendencies, or more simply, some guns' appearances puts a negative cast over the owner simply because it's "big, black, and ugly" or whatever.
So, perhaps you don't want to use the Punisher skull grips on your carry gun. Maybe you don't want to select a type of ammo that has "RIP" or "death-dealer" or something else sensational in its name. Maybe, maybe you don't want to show up in front of a jury after having shot a guy while strolling through your suburban neighborhood with an AR-15 pistol festooned with lights and lasers.
MAYBE.
But a common conversion barrel so your gun can shoot a slightly cheaper and/or less powerful round? It's going to be mighty hard for a prosecutor to get much of the superficial kind of "traction" they're looking for out of that.