To a large extent, dynamics are fixed on UPs. There’s an old joke about chainsaws having more dynamics than bagpipes. But this is not an absolute. As has been mentioned, you can lift the chanter off the knee for a slightly louder note, but you can often control this difference somewhat and mix it with a slur, giving a “swelling” effect. Also, you can play the same note with slightly more or less pressure. Depending on the reed, this can help to bring out or strengthen some of the overtones/harmonics on some notes. These are the sorts of subtle techniques that different pipers use to give them their own sound.
