Actually, its never even been implied that you needed to set something to your strife deck, in order to use it as a weapon, thats just head-canon. You can still use anything normally. It doesn't suddenly stop working. The strife deck is just an easier deck that restricts you to a single kind of item, but you can access it without having to go through the hassle of your Modus, making it ideal for weapons, which you generally need PRETTY FUCKING QUICKLY when something is attacking.
We have been arguing about this all day.
How about we leave it at this.
-Mod F