Under the zoning code, "retail sales and service" is different than office, but a zone that allows one use will usually allow the other.
A change of use, for purposes of the zoning code, may require bike parking, additional vehicle parking and/or changes to the parking, or paving and landscaping on the site. Exterior changes to a building, in many areas of the city, must go through a design review process to make sure that the proposed changes meet any special design guidelines for the area in which the project is located. The requirement for design review can be triggered by a very minor change, such as installing a replacement window that is not identical to the original.
For more information on how the zoning code would apply to your project call a Planner at (503) 823-7526.