You need to talk to your gas supplier and ask them how they provide their mixed gas. Some places provide mixed gas in a C02 cylinder and some provide mixed gas in a nitrogen tank. If they provide it in a C02 tank, you can just use your C02 regulator. If they provide it in a nitrogen tank, then your C02 regulator will not fit on the tank because it has a different fitting, but you can buy
this adapter to allow your C02 regulator to fit on the nitrogen tank.
A regulator doesn't really know or care what gas goes through it. All it is going to do is take a high pressure of any gas on one side and regulate it to a smaller pressure on the other side.