The board of supervisors of the county proposed to be annexed shall agree in writing with the board of directors of the district upon the terms and conditions of annexation, which agreement (among other things) may provide for the levy and collection of special taxes within the county in addition to the taxes elsewhere in this part provided for, the fixing of rates, rentals, and charges differing from those fixed or existing elsewhere within the district, the incurring or assumption of indebtedness, or the making of a payment or payments, or the transfer of property, real and personal, and other assets to the district by the county.