Repeal of a home rule charter shall cause the city affected by such repeal to revert to the form of government of such city immediately preceding adoption of the home rule charter and when positions to which officials were elected under the home rule charter are substantially the same as positions under the form of government to which the city reverts upon repeal, such elected officials shall continue to exercise the authority of such position for the salary prescribed by the home rule charter until expiration of their terms of office as prescribed by the home rule charter. No amendment of a home rule charter shall shorten the term for which any official was elected or reduce the salary of the official’s office for that term.