The city's seismic ordinance classifies the various building code occupancies into five "relative hazard" levels. Changing between office space (also a B occupancy) and retail space (an M occupancy) would not generally require a seismic upgrade, since B and M occupancies are classified at the same seismic hazard level.
Changing more than about 4,000 square feet from office to retail could require a seismic upgrade based on the increase in the number of occupants that the building code would assume.
Unreinforced masonry buildings (URMs) have some unique requirements under the city's seismic ordinance. Seismic triggers for URMS consider the work done to the building over time, and not just the current proposed work.
For more information on seismic triggers and your project, call a Life Safety Reviewer at (503) 823-1456.