Have just planted a small cherry tree and used it for the first time, the previous tree died so I am hoping this will give the new one a better chance.
I imagine if you are keen to use it, and you have really just planted the new shrub, you can do no harm, and maybe alot of good, by gently removing it and adding the fungus then replanting it. If just done it would not add a deal of extra stress to the plant, and the fungus may do a huge amount of good. I shall watch the cherry tree with interest.