I feed my shrooms all the time. You can drop a piece of pelleted fish food on their moouth and they will consume it. I made a tool that I use toload up with pellets and dispense a pellet or two or three at a time on each shroom, and they promptly ball up and consume it. I found that wh ile my shrooms did fine before I started to feed them, they do fantastic since I started to feed them. The grow faster, have much better color, and reproduce more.
Fragging shrooms is easy, just use a razor blade or sharp hobby knife and slice it into halves or quaraters with each portion having a section of the mouth. Use a hypodermic needle or syringe to stick em where you want them on live rock or frags of live rock, or just let em on the sand until the pick up some rubble and use super glue gel to stick that adhered rubble in place. Do not try to super glue a shroom with out saome sort of attached rubble or rock etc, as it will not stay. I prefer the hypodermic needle process as its quick and easy and is not an eyesore like netting and cages etc are.