It is called tap tuning and violin makers have been doing it for years. We don't know what Stradivarius, but nobody would be surprised by the claim that he was doing the same thing when making his violins.

There is however a lot of debate in the luthier community on if it actually matters. Some claim it does and spend a lot of time on it, and have even setup fancy test fixtures to show patterns with different frequencies. However some claim it makes no difference and [I'm not sure what]. Both produce great instruments.