This topic has been raised and debated on the list for hornplayers that I also subscribe to. There are repair shops that will cryogenically treat entire instruments in hopes of aligning the crystal structure of the metal. The upshot, as I recall, was that some claimed that they could tell the difference between before and after and some couldn't. Some of the metallurgically inclined on the list cited facts to prove or disprove claims of the process' efficacy, but no clear conclusion was agreed upon (big surprise). It is agreed that there is a measurable effect on the metals, but whether or not that amounts to a hill of beans when the metals are used and measured acoustically, is highly debatable (that's what listservs are here for, right?)
So, I am glad to have fully cleared all of that up <wry, wincing grin>. If anyone is particularly interested in this angle, contact me and I can search the hornlist's archives for the actual postings.
Regards,
Peter Hirsch