Within any rank, the municipal council or board of trustees of a civil service township may establish such special positions having special duties with preferential pay as the council or board deems necessary, but the holding of any such special positions shall not establish eligibility to the next higher rank to the exclusion of other persons in the same rank who do not hold such special positions. No special position established by council or the board within a rank in a fire department shall be filled without promotional examination in the same manner as promotions from rank to rank.