Final answer:
The most appropriate type of organizational effectiveness intervention to manage the change to dual reporting roles post-acquisition is Cultural alignment intervention.
Step-by-step explanation:
In order to manage the change to dual reporting roles post-acquisition, the most appropriate type of organizational effectiveness intervention to use would be Cultural alignment intervention. This intervention focuses on aligning the cultures of the three organizations and helping employees adapt to the new roles and collaboration. By addressing the strong opinions about competition's competencies and promoting a shared organizational culture, the intervention can help facilitate a smooth transition and successful integration of the acquired organizations.