Okla. Stat. tit. 82 § 612
The board of directors may at any time, when necessary to fulfill the objects for which the district was created alter or add to the official plan, and when such alterations or additions are formally approved by the board and by the court, and are filed with the secretary, they shall become a part of the official plan, but they shall neither materially modify the general character of the work, nor materially increase resulting damages for which the board is not able to make amicable settlement, nor increase the cost more than ten per cent (10%), no action other than a resolution of the Board of directors shall be necessary for the approval of such alterations or additions. In case the proposed alterations or additions materially modify the resulting damages or materially reduce the benefits, for which the board is not able to make amicable settlement, or materially increase the benefits in such a manner as to require a new appraisal, or increase the cost more than ten per cent (10%), the court shall direct the board of appraisers (which may be the original board, or a new board appointed by the court on petition of the board of directors or otherwise) to appraise the property to be taken, benefited or damaged, by the proposed alterations or additions. Upon the completion of the report of the Board of appraisers, notice shall be given in the same manner as in the case of the original report of the board of appraisers, and the same right of appeal shall exist. Provided, that where few land owners are affected, if found to be more economical and convenient, personal notice of the pendency of the report of said appraisers shall be given instead of notice by publication; and provided, that if the only question at issue is additional damages or reduction of benefits to property, due to modifications or additions to the plans, the board of directors, may, if they find it practicable, make settlements with the owners of the property damaged instead of having appraisals made by the board of appraisers. In case such settlements are made, notice and hearing need not be had. After bonds have been sold, in order that their security may not be impaired, no reduction shall be made in the amount of benefits appraised against property in the district, but in lieu of such reduction in benefits, if any are made, the amount shall be paid to the party in cash. This provision shall apply to all changes in appraisals under this act.
Okla. Stat. tit. 82, § 612