Prepared yellow mustard usually has extra flavorings in it. Often garlic as well as some other spices. Using it might affect the flavor of your recipe slightly. If you don't care about that then I dont' see why not.
Oh, you should also adjust your other liquids to compensate for the extra liquid in the mustard.
Yeah...I'm a bit worried about that. I'm making an egg dish.
You know the kinds that sits over night in the refrigerator. Made with
bread, eggs & cheese....
I make a dish that sounds similar to what I make and it calls for dry mustard I leave it out. To me it is better without it. My recipe calls for sausage and I tend to use the sweet sausage and it makes it a whole lot better.
I never add the dry mustard to my egg casserole, even though the recipe calls for it. I've never missed the taste, but then I'm not a big mustard fan anyway!
The good news is everyone loves it anyway! Leave it out and don't give it another thought