First and foremost, I should reassure you that the structure of those over-unders are designed to very effectively target assigned systems and elicit gains associated with that type of interval, so ending on an ‘under’ before moving to rest isn’t key when you’re considering the full scope of the workout.
Your question about custom workouts affecting future adaptations: custom workouts are not yet fully supported by Adaptive Training, and wont result in potential adaptations within your training plan in the way a completed TrainerRoad workout would.
Workout Levels V2 will account for all unstructured rides and workouts, and is being highly prioritized by the development team.