Having said that, the bed-and-breakfast is and R-1 occupancy group. 2007 CBC, Section 903.2.7 requires an automatic sprinkler system in accordance with Section 903.3. in all buildings with a Group "R" fire area.
You will need to get the historic resources report used to qualify the building for placing on the historic registry. The report will outline the nature of the building elements and composition required to be maintained or restored. Usually the ceilings where fire sprinklers are customarily installed is not a part of the historic "fabric" for maintaining or restoring thus sprinklers can be installed. There are quite a few new "tricks" for sprinklers to make them less noticeable, get in touch with a well qualified fire protection engineer.
Beyond the fire sprinklers you will need to address all the historic "fabric" for the conversion back to a residential use. Good luck