Cryogenic treatment brings nothing.

If a metal is being cooled down, the structure gets denser and the atomic activity deminishes. If it is cold enough, metal can be broken easily. But, as soon as the temperature rises, the activity resumes to the normal level, forcing the grid structure to go back to normal.
The other way round, heating and rapid cooling, does change the structure. In general this hardens the metal. This situation, however, wouldn't be stable, as the string is under tension and mechanically agitated.