The Board may, at any time, amend the Plan in whole or in part provided, however, that no amendment shall be effective to decrease or restrict the amount credited to any Account maintained under the Plan as of the date of amendment, nor shall any amendment be effective to decrease the Earnings Rate at which amounts are credited to any Account balance existing as of the date of amendment. Changes in the definition of “Earnings Rate” shall not become effective before the first day of the calendar year which follows the adoption of the amendment and at least 30 days written notice of the amendment has been given to each Participant.