Northern Mariana Islands Enhanced Nutrition Assistance Act of 2018 This bill amends the Agricultural Act of 2014 to reauthorize through FY2023 the pilot program for the Commonwealth of the Northern Mariana Islands to operate the Supplemental Nutrition Assistance Program (SNAP, formerly known as the food stamp program) in the same manner in which the program is operated in the states. The bill prohibits funds available for the pilot program from being provided for the Northern Mariana Islands nutrition assistance program block grant during a year in which more than $8.5 million in unexpended pilot program funds remain available for the grant.