The correct answer is D. According to U.S. Coast Guard regulations, if the maximum steam generating capacity of a boiler is increased, the vessel's officer in charge of the engineering watch must obtain a new Coast Guard-issued endorsement on their license, which is option D. The other options are incorrect because they do not accurately reflect the regulatory requirement to obtain a new endorsement when increasing the boiler's steam generating capacity. The Coast Guard needs to be notified of this change to ensure the officer's license and qualifications are up-to-date and match the vessel's equipment.