(a) The approval by the board of directors of the budget 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 be appropriated by subsequent action of the board 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.