After the budget hearings, the county commission may revise, alter, increase or decrease the items contained in the budget and may eliminate any item or add new items. If it increases the total proposed expenditures from any fund so that the total proposed expenditures exceed the total estimated income, it shall also make provision for the necessary additional income so that the budget as adopted shall provide revenue at least equal to expenditures for each fund. Any cash surplus at the end of any fiscal year shall be carried forward and merged with the revenues of the succeeding year. Payment of any legal unpaid obligations of any prior year, however, shall be a first charge in the budget against the revenues of the budget year. Except as herein provided, the budget shall be adopted and the appropriation order finally made at least ten days after the beginning of the fiscal year. At the same time, the county commission shall tentatively fix the tax rate necessary to finance and balance the budget. At the same time, also, a statement shall be prepared and made public showing the changes made by the county commission in the budget. The final tax rate need not be fixed until final action by the state tax commission on the assessment made by the county assessor. In any year in which the terms of any of the commissioners of the county commission in counties of classes one and two expire, the budget shall be approved and the appropriation order made by the new commission within thirty days after the beginning of the fiscal year.