Yes, if you update an exercise, it will be updated for all workouts that it appears in.
If you'd like to update a workout that is used in multiple places, you will be asked whether you'd like to save a new version or update all instances when you make edits to that workout.
Below is a quick screen recording of this experience:
If I edit an exercise, will it update for all workouts that it appears in?
Written by Matt Lawrie
Updated over 10 months ago