If multiple concession contracts are awarded to authorize concessioners to provide the same or similar outfitting, guiding, river running, or other similar services at the same approximate location or resource within a System unit, the Secretary shall establish a comparable franchise fee structure for those contracts or similar contracts, except that the terms and conditions of any existing concession contract shall not be subject to modification or open to renegotiation by the Secretary because of an award of a new contract at the same approximate location or resource.