Provided all fund balance reserved for unencumbered balances of appropriations for the prior fiscal year on hand at the close of day September 30, may be appropriated by supplemental appropriation to current expense purposes in the current fiscal year in the manner now provided by law. In the event of the recording of an estimated encumbrance or in the event of an increase in the cost price of supplies, equipment, materials, etc., these underestimations may be provided for during the three-months period by the cancellation of appropriations made by the county excise board prior to June 30, subject to the approval both of the governing board and the officer in charge of the department or appropriation account only in instances as hereinabove set forth and only in amounts sufficient to pay such increased encumbrances, and by reappropriation to the appropriation accounts in which an underestimate encumbrance was made, all in the manner as now provided by law for the making of supplemental appropriations.