I would not bother with the dry milk powder if you are using moss that is native to the area. Wait until fall or spring when the days are cool but humid to moist before making any transplants. When you do break up the surface of the soil and then press the moss sods into the new soil and then mist to lightly sprinkle thoroughly. You may want to prewet the soil and let its surface dry some before breaking it up to make plugging in the moss sods easier.
then just let it go and see what happens. It will take time so do not expect overnight success-it depends on the type of moss and how fast it grows. If a prostrate species it will cover faster than an upright species.