No, you should never pop a guitar blister. These swellings are filled with blood serum, so they will start to bleed and risk getting infected if you pop them. Blisters actually act as a protective barrier that can help prevent infection and promote healing. If the blister has already popped or broken on its own, you need to keep the area clean and covered. Apply a sterile bandage or adhesive tape to protect the blister from further irritation and keep it dry.