Class mod skill bonuses do stack, even if a specific skill is maxxed (5/5). They are class specific upgrades that provide benefits to the character (or the entire team) by offering a wide variety of bonuses such as amplifying a character's damage, healing, increasing character health or shield capacity, reducing reload times, increasing skill ranks, etc. 1 Borderlands: The Pre-Sequel Class ModsĬlass Mods, or COMs (short for Class Optimization Modules), are influential items in Borderlands: The Pre-Sequel.