I would say yes. You may be able to classify it as an accessory occupancy, but really you still have a change of occupancy.
Also, take note that the IEBC has both a change of use and a change of occupancy.
[A] CHANGE OF USE. A change in the use of a building or a portion of a building, within the same group classification, for which there is a change in application of the code requirements.
[A] CHANGE OF OCCUPANCY. Any of the following shall be considered as a change of occupancy where the current International Building Code requires a greater degree of safety, accessibility, structural strength, fire protection, means of egress, ventilation or sanitation than is existing in the current building or structure:
- Any change in the occupancy classification of a building or structure.
- Any change in the purpose of, or a change in the level of activity within, a building or structure.
- A change of use.
Scoping of applicable sections is dependent upon change of use/occupancy, and is as follows:
2021 IEBC
1001.2.1 Change of Use
Any work undertaken in connection with a change in use that does not involve a change of occupancy classification or a change to another group within an occupancy classification shall conform to the applicable requirements for the work as classified in Chapter 6 and to the requirements of Sections 1002 through 1010.
Exception: As modified in Section 1204 for historic buildings.
1001.2.2 Change of Occupancy Classification or Group
Where the occupancy classification of a building changes, the provisions of Sections 1002 through 1011 shall apply. This includes a change of occupancy classification and a change to another group within an occupancy classification.
1001.2.2.1 Partial Change of Occupancy
Where the occupancy classification or group of a portion of an existing building is changed, Section 1011 shall apply.
Take note that the most significant requirements come from Section 1011, which only applies to Change of Occupancy.