The employer may amend this plan at any time or from time to time by an instrument in writing executed in the name of the employer under its municipal seal by officers duly authorized to execute such instrument and delivered to the Council; provided, however:
A.
That no amendment shall deprive any participant or any beneficiary of a deceased participant of any of the benefits to which each is entitled under this plan with respect to contributions previously made;
B.
That no amendment shall provide for the use of funds or assets held under this plan other than for the benefit of employees, and no funds contributed to this plan or assets of this plan shall, except as provided in § 57-193, ever revert to or be used or enjoyed by the employer; and
C.
That no amendment to the plan which provides for a benefit modification shall be made unless the cost estimate described in § 57-197 has been prepared and presented to the Council in accordance with the Act.