The National Register is a list of buildings, sites, and districts designated as important in American history, culture, architecture or archeology. It is a federal designation administered by the Secretary of the Interior through the Massachusetts Historical Commission. If your property is listed in the National Register you may do anything with it you wish.
Listing in the National Register:
Recognizes that the area is important to the history of the community, state or nation
Allows the owners of income-producing properties certain federal tax incentives for renovation
Provides limited protection from adverse effects by federally funded, licensed or assisted projects
In no way limits the owner's use of the property unless public funding is used