Can the Accountable person be changed in an action?

Yes, the person assigned as 'Accountable' for an action can be changed. To do this, open the action record and edit the details directly. This is generally possible if the action is in a Draft, Open, or Overdue state. 1

When creating a new action, responsibility is assigned using both the 'Accountable' and 'Assigned to' fields. The 'Accountable' person is responsible for ensuring the action is completed, while the person it is 'Assigned to' is responsible for carrying out the work. 2