Subsequent to the public hearing provided for in Section 7-11 and before final action on the budget, the board may revise, alter, increase, or decrease the items contained therein, but the aggregate amount finally appropriated by the budget, including any subsequent amendment thereof, from any fund or for any purpose, including amounts appropriated for judgments and all other unpaid liabilities and all other purposes for which such authorities are herein or otherwise by law required to appropriate, may not exceed the aggregate amount available in that fund or for that purpose, as shown by the estimates of the available assets thereof at the beginning of that fiscal year and of taxes and other current revenues set forth in the budget. If the appropriations from any fund as set forth in the budget as finally adopted exceed in the aggregate the maximum amount which the board is authorized to appropriate therefrom, all appropriations made from that fund by the budget are void and the several amounts appropriated in the budget of the last preceding fiscal year, so far as they relate to operation and maintenance expenses, shall be considered to be appropriated for the current fiscal year for objects and purposes, respectively, as specified in the budget for the preceding fiscal year and the several amounts so appropriated shall constitute lawful appropriations for the current fiscal year. The board shall cause the budget to be entered in its proceedings within 10 days after its passage.