Project manager and project team
The project board will ultimately choose whether changes are executed or not and it will then be the responsibility of the project manager to make the revised versions of the plan and get them circulated to all project team members.
During the project, it is the responsibility of the project manager to motivate team members so that the tasks assigned are done in line with X Company's project objectives. The project manager will have direct responsibility for the work assigned to every team member, the responsibility every member is given and the recognition they are accorded on completion of this work.