Explanation
Using a validation rule on Opportunity Products can prevent a sales rep from adding Products marked as requiring the myTrailhead badge if the rep has yet to complete the badge. The validation rule can check the value of a custom field on the Product object that indicates whether the myTrailhead badge is required, and compare it with a custom field on the User object that tracks whether the sales rep has completed the badge. If the validation rule evaluates to true, it can display an error message and block the addition of the Product.
Using a separate price book for the Products requiring the myTrailhead badge and only sharing the price book with sales reps who have completed the badge can also validate that sales reps have completed the myTrailhead badge. The price book can contain only the Products that require the badge, and it can be shared with sales reps who have a custom field on their User record that indicates they have completed the badge.
This way, only those sales reps can access and add those Products to their Opportunities.