My acoustic upright piano is 110 years old, made in 1910. Last time I had it tuned, the tuner used a 440 Hz tuning fork and tuned it by ear, but he broke my B♭7 string. If a piano is not used in an orchestra, but only home use, wouldn't it be better to tune middle A to 432 Hz (Verdi's A) which better resonates with the fundamental 8 Hz Schumann resonance? This lower tuning might sound better and extend string life.
It might extend string life, and it might make the piano sound rather dull since the strings may be designed for the tension at which A is 440 Hz or even higher. Whether it's better is a matter of opinion.
The fact that Verdi used 432 Hz (if that is in fact true; this is the first I've heard of it) has very little bearing on the tuning of a piano unless it is a piano of Verdi's time. It might also be of interest for singers of Verdi's music.
The fact that 432 is differently resonant with 8 Hz than is 440 Hz is not relevant in the least. The number is just an arbitrary standard based on an arbitrary unit of time. The second is hardly a fundamental constant of nature.
As Tim points out in his answer, if an old piano's pitch is low, it might be a good idea to leave it low. Whether 432 is a good frequency for A would really depend on the piano, not on any fanciful numerological ideas.
When playing period music, on period instruments, they are tuned to the standard of that time, if at all possible. Partly to be authentic, mostly to be kind to the instruments. Understandably.
Given that your piano is old, thus the strings probably are too, any Hz lower than 440 will be kinder. There's no good reason to use 432Hz, though. If it was mine, I'd probably go for making B♭ 440Hz. Then at least I could play along with the majority of stuff that's recorded or on the radio - or even along with others that were concert pitch tuned - albeit a semitone out. But that's me.
From your position, any lower tuning would suffice, although there would come a point where the strings were too loose, and sound quality would suffer. I guess that's where tuning experience comes in. An awful lot of older pianos never get back to their original concert pitch, tuners are happier to leave then slightly under, for many good reasons.
Thus - if it's dropped slightly, just get it tuned to itself at that pitch. 440Hz, 432Hz, 428Hz, whatever, it'll still work. Back in the '60s, guitar bands would tune to whoever was best in tune already - that didn't stop things sounding good, even if it was 'in the cracks'!
If an acoustic piano is required to play with other instruments tuned to concert pitch then it will be better to tune the piano to 440 Hz. If the piano is not going to play with other musical instruments ( other than voice ) then it can be acceptable to tune it to 432 Hz assuming the piano tuner has a 432Hz tuning fork. Next time I get my piano tuned I may ask for the 432 Hz = middle A just to check out any difference in the harmonies and resonance.