Haven't read Corps Instructions for a while (will do so when I get in to work later), but in my day WO1's had the choice whether to wear Offrs pattern Mess Dress which as far as I can remember was a jacket with eppauletts & cloth badges instead of collar dogs.
Shirt, tie, Shoes & hat would refer to Service Dress, not Mess Dress IMO, dispensation is also given for a WO1 to wear a cloth cap badge on his/her beret.
As the big badge bloke you can wear whatever you like as long as you have had the chat with the RSM and given him the nod. Just call it a tradition from one of the Regt's you served with and you get away with lots!!