They could through the Criminal Code regulations. So the Governor in Council could no longer downgrade the classification of a firearm. The power to downgrade was exercised twice in 2015 in relation to these firearms. The government is seeking, through Bill C-71, to give up or rescind that power, asking Parliament to take that power away from the Governor in Council. In the two instances where it was used, you question why the grandfathering would come in. The grandfathering comes in in those cases to allow the continued ownership by people who have bought those firearms in good faith under the existing rules of the day.
On June 7th, 2018. See this statement in context.