I haven't done it but I do see people do it all the time. No big deal. Bring it I doubt they will say anything to you. Really what could they say.
I thought it was just me... we pack cereal bars, oatmeal (I boil the water in the coffee maker and then pour in, or just get hot water from the hot water dispenser at the food court).We ALWAYS bring our breakfast. We're not huge breakfast eaters so we'd prefer to use our cs credits for lunch or dinner. We bring granola bars, dry cereal and pop tarts usually. Ocassionally my dh will bring back a box of doughnuts for breakfast when he goes to get our drinks in the mornings.
Just run water through the coffee maker. This way some people can eat, while others are getting dressed. I wouldn't make the walk all the way to the food court.
They could tell you that the microwave is for food that was purchased AT the food court, not your own private food.