A design structure embodied in a machine-readable medium is disclosed in one embodiment of the invention as including a flexible logic block to facilitate engineering changes at selected locations within an IC. The flexible logic block has a consistent and identifiable structure such that a simple automated process may be used to reconfigure the structure to perform different logical operations. In certain embodiments, the flexible logic block includes a circuit, such as a multiplexer, having multiple inputs and at least one output. A metal interconnect structure is coupled to the inputs and enables connection of each of the inputs to one of several electrical potentials using a focused-ion-beam (FIB) tool. In this way, the circuit may be configured to perform different logical operations after components in the IC exist in hardware.