Currently, in the example you used, if the classification of a firearm changed to a more restrictive classification, businesses would be required to have that business condition on their licence to possess those types of firearms. If they do have those conditions on the licence to possess those types of firearms for that prescribed purpose, then they could continue to own those firearms. If they do not have the prescribed purpose, then they would have to have the firearms removed from their inventory—for example, by export sale to another business that does have that prescribed purpose.
On June 5th, 2018. See this statement in context.