After a construction contract is awarded, if the district determines that additional work is needed or if the character or type of work, facilities, or improvements should be changed, the board may authorize change orders to the contract on terms the board approves. A change made under this section may not increase or decrease the total cost of the contract by more than 25 percent. The board may grant authority to an official or employee responsible for purchasing or for administering a contract to approve a change order that involves an increase or decrease of $50,000 or less.