§ 54. Modification of alternative form after adoption. A county which shall have adopted an alternative form of county government may, in like manner and with like approval of the electors of the county, as provided by this chapter for submission and adoption of an alternative form of county government, supplement the form of government theretofore approved by adding thereto any provisions which might have been adopted originally or delete or change any provisions of the form so as to leave it in a modified form which could have been adopted originally, and the form of government as thus modified shall, from and after the time it becomes effective, have the force and effect of, and be deemed to be, an alternative form of county government.