"When substantial changes are to be made to the plan (typically, for new employees), consideration should be given to adopting a whole new plan (on which a determination letter could be obtained), rather than amending the existing plan to create a new benefit structure. Plans adopting novel benefit structures may seek private letter rulings dealing with the new benefit structure.... In the event of a corporate acquisition or merger, it will become critical to obtain ironclad assurances from the seller that all retirement plans are qualified.... In some instances, it may make sense to have old plans terminated before the merger or acquisition."