I think we can definitely say that the piano is a symbol that changes in this excellent short story that focuses on the relationship between a mother and her daughter. It is clear that from the first mention of piano lessons, the piano, in Jing-Mei's childhood, is a symbol of the conflict between the mother and the daughter. Note Jing-Mei's initial response to the news that she will be having piano lessons:
"Why don't you like me the way I am? I'm not a genius! I can't play the piano. And even if I could, I wouldn't go on TV if you paid me a million dollars!" I cried.
Thus we can see that even before Jing-Mei touches a piano, it is a symbol of the tension in her relationship with her mother and the way that she feels pressurised into being something that she is not. This of course continues as she has lessons with Old Chong, who can't actually hear, and then gives her disastrous performance.
However, at the end of the story, once Jing-Mei has asserted her own will and her right to "fall short of expectations," she is given the piano back by her mother, which Jing-Mei herself sees as a "shiny trophy" that she had won back and as a symbol of "forgiveness, a tremendous burden removed." The symbolism of the piano has changed subtlely because now Jing-Mei has won it on her own terms, without having to be pressurised. It also symbolises the way that Jing-Mei's mother accepts her for who she is as well.