Absolutely! If you want to change a specific set of exercises in your workout, tap the i button at the bottom right of the set card when you start the workout, then tap Replace. You'll be given two alternative sets to choose from, one harder and one easier. You can also swap out a set while you're working out by tapping Pause (top right button) and then the i button at the bottom right of the set card for the exercise you want to replace.