Are you sure this is correct? The IEBC 2015 Code and Commentary - Chapter 10 - General Comments states that:
"As a general rule, when a change of occupancy classification occurs, the requirements of Chapter 9 for Level 3 alterations apply, along with all of the provisions
of Section 1012. However, there are exceptions to this rule as well, as provided in Section 1012.4, which deal with a change of occupancy where the change is clearly to a lesser hazard."
Did something change in the 2018 edition?
The question was whether the "Change of Occupancy" is
the classification or if any other classification would also apply. Only one classification applies, but other requirements for other classifications may be applicable. For example, a "Level 3 Alteration" requires compliance with Levels 1 and 2, but you do not refer to it as a "Level 1, 2, and 3 Alteration," you just call it a "Level 3 Alteration." The same applies to a change of occupancy. You would classify it as a "Change of Occupancy" (which, as you pointed out, requires compliance with some requirements for Level 3 Alterations), and not as a "Level 3 Alteration, Change of Occupancy."
Regarding the
Commentary's statement that "As a general rule, when a change of occupancy classification occurs, the requirements of Chapter 9 for Level 3 alterations apply," I find this blanket statement somewhat misleading. Chapter 9 (Alterations -- Level 3) is only applicable to the extent it is referenced in Chapter 10.
Section 1012.1.1.1 (2015 IEBC) requires compliance with Chapter 9 throughout a building when the fire protection threshold is different per the IBC and the change of occupancy work area is not separated from the rest of the building with fire barriers. In this case, the "Change of Occupancy" classification is applied to the area where the change of occupancy occurs, and the rest of the building would be classified as a "Level 3 Alteration."
If the change of occupancy work area is separated per Section 1012.1.1.2, the application of Chapter 9 only applies to the change of occupancy work area. Thus, the work area is classified as a "Change of Occupancy" and the rest of the building, or portions thereof, are classified according to their types of work.