Tuscany-Canterbury is a National Historic District. This does not prohibit any changes to the outside of the property.
Tuscany-Canterbury IS NOT a CHAP (City Historical and Architectural Preservation) District: That means you do not have to get approval from Baltimore City before making changes to the outside of the property. (Color, roof, doors, windows, fence, deck, etc)
Deeds in Tuscany-Canterbury have NO COVENANTS that restrict the outside appearance of your home.
Tuscany-Canterbury does have SUGGESTED GUIDELINES about changes to the outside of the property. See https://tuscanycanterbury.org/neighborhood-association/architectural-guidelines/. These are suggestions only.
Baltimore City requires permits on certain types of work and these are required on all properties in Baltimore City. Some work may require zoning changes (for example adding an addition, extending a deck into the setback area).