In the 2006 International Building Code you are required to apply for a Change of Occupancy whenever a building (or portion of a building) moves from one occupancy category to another. In other words, even if you are not making changes to a building but you are changing the use of a space you may need to apply for a change of occupancy.
For this process, the building needs to meet the requirements for the new occupancy. Where they are more restrictive than the existing requirements it may mean upgrades.
The building official is allowed to approve the change of occupancy without changes to the building where the new occupancy is less hazardous than the existing use.
This is actually fairly common where spaces are moving between offices, retail and restaurant/bar (assembly) uses in a strip center. It is advisable to consider designing these commercial building types where they can take the most hazardous occupancy.
It is also a big consideration in looking at space for your business if the previous use was lower hazard.
If you think this might apply please contact me for clarification.