John Tuttle inquires, "If a circa 1880's grand piano with highly carved
legs gets damaged and a new leg is manufactured (carved) to replace the
damaged leg, is the piano still considered an antique?"

Absolutely!  A buyer might want to know that one of the legs has been
remanufactured, as the piece is not as "original" as one that has not
had such a replacement, but it certainly is still an antique.

Now the interesting question:  How many pieces or parts can you
remanufacture and have it still be an antique?  Who knows?  When you
rebuild a player mechanism, and, for example, "improve" the pouches
by using kangaroo leather, is it still an antique?

In the classic car hobby, radiators are replaced, engines are rebuilt
with modern parts, even fenders replaced with new ones.  They're still
classic antique cars.  When the car is "rebodied", however, the classic
car club makes such notation with the car's registration.  Rebodying
becomes quite profitable when you can throw away a sedan body and
replace it with a brand new phaeton body, and increase its value from
$25,000 to $250,000.

Ray Fairfield