Sometimes there are certain slurs or dynamic markings in piano music that just don’t feel right, no matter how you try to make them sound convincing. Here’s an article that just might put your mind at ease when you decide to tweak a piece to fit your own interpretation. According to Byron Janis –
In 1960, I opened the cultural exchange between the U.S. and the Soviet Union, and brought Aaron Copland’s Piano Sonata to play. Never having performed it before, I wanted to play it for the composer first. On arriving at his home, I found him tinkering with one of its passages and said, “Mr. Copland, I notice you are playing forte and you have marked it piano in the score.” He turned to me grinning mischievously and said, “Ah, but that was 10 years ago!”
Some 200 years earlier, Chopin would have made a similar remark. Only he would have said, “but that was 10 seconds ago!” Julius Seligmann, president of the Glasgow Society of Musicians, attended a recital where the composer played his new “Mazurka in B flat, Opus 7 no. 1” as an encore. According to Seligmann, it met with such great success that Chopin decided to play it again, this time with such a radically different interpretation—tempos, colors and phrasing had all been changed—that it sounded like an entirely different piece. The audience was amazed when it finally realized he was playing the very same mazurka, and it rewarded him with a prolonged, vociferous ovation. It seems he had facetiously decided to show why he had no need to republish a score—the magic of interpretation would do it for him. He would often say, “I never play the same way twice.”
Read more here.