Drip acclimating corals can be harmful and kill them, all you need to do is temperature acclimate and toss them in. You can frag your mushroom whenever, the thing is the frags will be small and take time to get to full size so you may end up better off with just letting it grow on its own. Unless it's a really expensive type of mushroom you'll probably find yourself a year down the line wondering what you're going to do with your 300 mushrooms.