"Like any other material plan design choice, the decision to do a backsweep of current employees and/or to re-enroll participants in a QDIA involves a combination of finance, human resources, employee communications, and other concerns. However, concerns about legal risk should not be an impediment to these actions. Various 'safe-harbor' provisions of ERISA enacted as part of PPA '06 affirm the legality of both backsweeps and re-enrollments, as long as specified required steps are taken to comply with those safe-harbor provisions[.]"