We are thinking about trying for lunch at LC on our upcoming trip, but I really want to try the filet, and the only one I see on the menu is the mushroom filet with mushroom risotto. I hate mushrooms! Can I get it without them and get the mashed potatoes instead? Thanks!

You can ask for ANYTHING to be changed anywhere on Disney property and I've never heard of being told no. 
I am so happy to hear that subsitutes are available. My DH hates that I always (I MEAN ALWAYS) have to order a dish with this or that left off or added he says I am so high maintenance when it comes to food.