Is It Possible To Change Or Effect The Sound?

Is it possible to change or effect the sound after you play a key? i think when the hammers stroke the strings, it is impossible to change the sound? IS IT POSSIBLE TO GAIN 2 DIFFERENT TIMBRES from 2 DIFFERENT PLAYERS at the SAME PIANO? we all see some pianists that doing artistic movements on the keyboard after playing the notes their arms are dancing any opinions?