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I have found this question hard to answer. A previous post on this forum worded, "Is 432HZ more "natural" or beneficial to human body than 440Hz?" What not satisfactorily answered, I think largely because the question was to vague. What is meant by "more natural" or "more beneficial".
I thought rephrasing the question to make it more concrete might provide better insight. What reasons are there that might prompt sound technicians to tune to 440Hz instead of 432Hz?
The older 'standard' appears to be a French one at 435Hz.
While, 432Hz was used by Verdi; also referred as 'Verdi Tuning',
based on a power of 2 calibration for middle C.
The ISO 16 standard finalized to 440Hz (among other variations;
including 439Hz being a prime and hence not easily reproduced in the lab).
So, I guess it is not quite like 432Hz was changed to 440Hz
(you could probably say 435 was changed to 440... yet, there is a lot of detail on Wikipedia about this).
Extracts from the Wikipedia page on Concert Pitch.
The A above middle C is often set at 440 Hz although other frequencies are also used, such as 442 Hz and 443 Hz. Historically, this A has been tuned to a variety of higher and lower pitches.
And, there is a lot of other interesting information there and on linked pages about its variations.
The most vocal opponents of the upward tendency in pitch were singers, who complained that it was putting a strain on their voices. Largely due to their protests, the French government passed a law on February 16, 1859 which set the A above middle C at 435 Hz. This was the first attempt to standardize pitch on such a scale, and was known as the diapason normal.
and after that,
The diapason normal resulted in middle C being tuned at approximately 258.65 Hz. An alternative pitch standard known as philosophical or scientific pitch, fixed middle C at 256 Hz (that is, 28 Hz), which resulted in the A above it being approximately 430.54 Hz. The appeal of this system was its mathematical idealism (the frequencies of all the Cs being powers of two). This system never received the same official recognition as the French A = 435 Hz and was not widely used. In recent years, this tuning has been revived, sometimes as 432 Hz under the name "Verdi tuning" since Italian composer Giuseppe Verdi had proposed a slight lowering of the French tuning system.
