Any Class 7 municipality operating under a commission form of government with its members elected at large and which at large system has been decreed to be in violation of the federal Voting Rights Act by a court of law may, by an ordinance duly adopted not less than three months prior to the regular municipal election, adopt a mayor-council form of government with the mayor elected at large and a five-member council elected from single-member districts. The ordinance shall divide the municipality into five single-member districts of nearly equal population and shall provide that candidates for election for a place on the council shall have resided within the district from which he or she seeks election for a period of 90 days immediately preceding the date of the election, and shall continue to reside in the district he or she represents so long as he or she remains a member of said council. Only electors residing within a district shall be entitled to vote for candidates seeking election for said district.