Do I have to do the cross-training prescribed?
Cross training workouts are specifically assigned in your plan. If you expand the day these workouts appear, you'll find a detailed PDF with how-to instructions, research on the benefits, and specific workouts.
Of course, we can't cover all the possible cross training modalities. In your plan we have included the most common and research-backed methods. If you want to sub in your own, preferred method of cross training, feel free.
Cross training is optional. If you want to switch an off day with another cross training day, that's fine. If you want to change the type of cross training, that's ok to.