harold wrote:...urban legends:
A few that were conspicuously missed:
1. Replacing the valve caps on your axe with extra heavy duty ones will do something other than make your horn heavier.
2. A well regarded repair guy on this board has stated that filling the air pocket in the guard mouldings and the guard wire will darken the sound on a horn.
3. Cryonics does something other than lighten your wallet.
Your item #1 was tested in the Rick Denney Mythbuster lab several years ago, and this myth was not at all busted. The heavy caps on the rotary tuba made a significant and noticeable difference, when tested by two players and three listeners. The instrument was a little less flexible with slightly better slotting. The change was thought to be an improvement by one player (me), and not an improvement by the other player (TubaRay). We both agreed that it helped me and hindered him. The test mule was a Miraphone 186, and the weights were Monsterweights.
From the point of view of science, adding significant mass to the instrument can indeed significantly affect the resonance of the brass, and the resonance of the brass can indeed affect the sound, but both are subtle. I doubt anyone would be able to hear a difference in the tone color, but there was a difference in the attacks as a result of the change in responsiveness of the instrument. More significantly, adding mass changes the frequency and magnitude of vibration of the instrument as felt thorugh the hands and as a sound radiator close to the player's ear. Those effects are real and have an effect on the player's sense of what is being played.
The Rick Denney Mythbuster Lab has also tested the effect of filling guard molding with solder. I performed that test on my project tuba, and did not notice much difference on that instrument. But it's the same issue of adding mass to the instrument. If you add mass to, say, the pendulum of a clock, you won't change it's period (unless you change the length to the center of gravity), but you will significantly affect both the impulse required to keep it swinging and the arc of the swing.
The idea behind cryogenic freezing is that it relieves the internal stresses of the instrument that were introduced when the parts were worked. The Rick Denney Mythbuster Lab hasn't tested that notion, and thus skepticism abounds. But let me ask this: Do you think baking an aluminum bicycle frame at 350 degrees for 15 hours after it is welded will significantly change the fatique durability of the metal? Aluminum has a melting point of what, 1400 degrees? How could 350 degrees be hot enough to relieve stresses? But it is.
Here's a myth for you: Tuba harmonics work just like a straight organ pipe.
Rick "not queueing his tuba up for cryogenic treatment, and think it's too subtle an effect to actually sense, but not dismissing it out of hand, either" Denney
Perhaps he meant to write: "Swinging WITH cats..." 
