I have removed many mushrooms from many rocks. I lay a couple towels down on the floor, take the rock out of the tank and place it on the towels, grab a flathead screwdriver and a hammer, and carefully chisel off the small portion of rock that the mushroom is actually attached to.
Sometimes you will get most of the mushroom off, but a small portion will still be connected to your main rock. You can cut that connection, leaving a small amount of the mushroom attached to the main rock still, and in time it will grow to another perfectly healthy individual (whether it has a portion of the mouth attached to it or not). That being said, I have never tried cutting a Yuma this way, I know they are a lil more sensitive than most mushrooms, but mushrooms as a whole are pretty hardy.
Hope this helps. I've fragged a ton of mushrooms...you can significantly increase a colony pretty easily...with a lil bit of patience
Oh...and massaging the foot won't work for mushrooms