(a) The approval of the budget by the board of directors shall amount to an appropriation, for the purposes of the budget, of the funds which are lawfully applicable to the different items therein contained.
(b) The board may alter or revise the budget from time to time, and unpledged funds appropriated by the board for any specific purpose may by subsequent action of the board be appropriated to another purpose subject to the following exceptions:
(1) Funds resulting from taxes levied under statute or ordinance for a specific purpose may not be diverted to another purpose; and
(2) Appropriated funds may not be diverted to another purpose where any creditor of the municipality would be prejudiced thereby.