My answer would be that as a lawyer I don't know what else I could add to what Mr. Fraser just said.
I would only say that a preamble is not necessary, but it provides information about the scope of the bill. Also, it provides directions to the Governor in Council. If the Governor in Council adopts regulations to add some position, then the preamble circumscribes the discretion of the government as to the position it would like to add to the list of the 10 positions. It provides the intent of the legislator and defines the scope of the Governor in Council's power to add positions to the list.