The one-count indictment against Yongda Huang Harris, 28, replaced an original charge of transporting hazardous materials.
If convicted of the new charge of making false statements, Harris could face up to five years in prison.
Authorities said Harris lied on his customs declaration by not stating that he visited Japan and by stating he had only $100 in items purchased abroad.
His attorney Michael Rosenstein declined comment.
Harris was arrested Oct. 5 on a trip from Japan to Boston. He was wearing the bulletproof vest under a trench coat along with fire-resistant pants and kneepads.
His attire attracted the attention of law enforcement, and when his luggage was checked the weapons cache was found, authorities said.
The search also revealed a hatchet, knives, collapsible baton, handcuffs and other items that were permitted to be transported in checked bags.
Prosecutors, however, said the items looked like a kidnap kit. They said at a court hearing last month that Harris had files on his computer detailing how to kidnap and kill people.
The circumstances involving the smoke grenade remained under investigation. Authorities have said it falls into a category of items prohibited on passenger aircraft.