Abstract: An existing design of an integrated circuit includes existing cells that have already been placed and routed. An engineering change order (ECO) specifies additional new cells (ECO cells) to be inserted into the existing design. The ECO cells are also associated with target locations for their placement among the existing cells, but these target locations may violate design rules. The feasibility of “legalizing” the placement of the ECO cells within the existing design is assessed as follows. The ECO cells are clustered into clusters based on their target locations. Clusters are assessed by determining an ECO placement impact (EPI) index for individual clusters. The EPI index is a measure of the feasibility for legalizing the placement of the ECO cells in that cluster.