mixed use: 508.4 change of occupancy classification?

i’m missing something. 302 - 311 describes CLASSIFICATION. table 508.4 is required separation of occupancy. so if a problem says you need to put “storage” room next to a “utility” space, tell me what is the required separation. then i find U and i find S and i see it says N for no fire separation required. what do i do if it says that it used to be U and S but my client is converting the discs and wants to have some random confusing occupancy (frog dissection classes or whatever) next to some other random occupancy (herbal necklace maker or something). am i digging around in chapter 3 trying to find appropriate classification for these uses? am i trying to find a overall building classification and trying to verify both these uses fall under accessory occupancy or non-separates occupancy? i guess i’m confused here. THANKS