A method is disclosed for improving design criteria and importantly timing criteria following a metal-only engineering change. The method involves making initial logical changes involving new books (gate-level, filler-cell circuits, called `eco books`), running placement and routing with the new books, and timing the resulting logic. If there are timing violations, existing, non-filler books which are in close proximity are considered for swapping with the eco books. The book swaps are all done with wire connections only (i.e. the book placements are not affected). This way, critical paths and non-critical paths can be traded-off to achieve a faster design, even though books are not allowed to be moved. Some simple algorithms are discussed; however, there are many heuristic and analytic algorithms that can be applied in choosing swaps, based on the needs of the particular design.