An urban renewal plan may be modified at any time by the governing body: provided that if modified after the lease or sale by the municipality of real property in the urban renewal project area, such modification may be conditioned upon such approval of the owner, lessee, or successor in interest as the municipality may deem advisable and in any event shall be subject to such rights at law or in equity as a lessee or purchaser, or his successor or successors in interest, may be entitled to assert.
SDCL 11-8-19