A system for modifying properties of an article of footwear is disclosed, wherein the article of footwear includes a removable foot-supporting member that includes a frame portion that defines an aperture, one of a plurality of insert portions that are received by the aperture, and a restraining member attached to an upper surface of the frame portion. By removing the insert portion, which has a specific physical characteristic, and replacing it with an alternate insert portion, which has a different physical characteristic, properties of the article of footwear are modified. The restraining member is attached to the upper surface of the frame portion, but not to the upper surface of the insert portion. The restraining member prevents upward movement of the insert portions and stretches to accommodate insert portions having various dimensions.