Any county which has covenanted with landowners of farm or forest land as to assessments and open space use of such land under the act of January 13, 1966 (1965 P.L. 1292, No. 515),¹ entitled “An act enabling certain counties of the Commonwealth to covenant with land owners for preservation of land in farm, forest, water supply, or open space uses,” may, at the landowner's option, renegotiate such agreements so as to make them conform to the provisions of this act as to preferential assessments.