The management of irreparable rotator cuff tears presents significant challenges, particularly in active individuals experiencing functional limitations, such as reduced forward elevation and deficits in both external and internal rotation. Traditional latissimus dorsi (LD) tendon transfer has shown effectiveness in reducing pain associated with posterosuperior cuff tears but often yields inconsistent functional outcomes. This is largely due to the LD's primary role as an internal rotator, which limits its capacity to restore normal shoulder biomechanics. To address these limitations, the lower trapezius (LT) tendon transfer, augmented with an Achilles allograft, has emerged as an alternative to enhance external rotation, leveraging the LT's line of pull, which closely resembles that of the infraspinatus muscle. This protocol outlines a modified surgical technique for LT tendon transfer with Achilles allograft augmentation, detailing patient positioning, tendon harvest, graft preparation, arthroscopic passage, and fixation methods. The protocol emphasizes key anatomical landmarks to minimize neurovascular injury and enhance graft integration. Postoperative care includes a 3 month immobilization period followed by a structured rehabilitation program to facilitate functional recovery. This procedure is indicated for a specific patient group requiring improved external rotation and is biomechanically advantageous over the LD transfer. Though additional studies are warranted to confirm its efficacy in broader patient populations, early clinical outcomes suggest that LT transfer with Achilles allograft could offer superior biomechanical alignment and improved external rotation.