When a sore is almost healed, and if a person rips or tears it open, it is way of preventing the healing process and further aggravating the pain. This phrase, metaphorically suggests, to revive or reopen a quarrel or enmity which was almost forgotten.
Thinking out of the box is thinking in a creative way. However, it can also be used for a ready-made product that requires no specialist knowledge to set it up.