((a)) The corporation shall provide by regulation for the reduction or waiver of liability for a complete withdrawal in the event that an employer who has withdrawn from a plan subsequently resumes covered operations under the plan or renews an obligation to contribute under the plan, to the extent that the corporation determines that reduction or waiver of withdrawal liability is consistent with the purposes of this chapter.

((b)) The corporation shall prescribe by regulation a procedure and standards for the amendment of plans to provide alternative rules for the reduction or waiver of liability for a complete withdrawal in the event that an employer who has withdrawn from the plan subsequently resumes covered operations or renews an obligation to contribute under the plan. The rules may apply only to the extent that the rules are consistent with the purposes of this chapter.