Tropical Forest Conservation Reauthorization Act of 2018 This bill reauthorizes the Tropical Forest Conservation Act of 1998 through FY 2020 and expands the Act to include coral reefs as well as tropical forests. The bill also changes the name of the Act to the Tropical Forest and Coral Reef Conservation Act of 1998. The bill authorizes to be appropriated funds for the Act's debt-for-nature swaps and debt buyback programs through FY 2020. Such programs convert reduce or convert debt obligations from eligible countries to the United States into funding for nature conservation and protection efforts in that country. The Tropical Forest Facility, an entity that administers the programs, shall be renamed the Conservation Facility. The bill modifies the administration of agreements signed between the United States and each country that participate in the debt reduction programs. The administering body for each country that disperses grants under the Act shall have at least one U.S.-appointed individual serving in an official capacity. It also modifies the additional approval requirements for larger grants and defines such grants as those of more than $250,000. Currently, grants of more than $100,000 are subject to additional approval requirements.