I think that washing the roots and planting the tree without damaging the roots is a really hard trick to pull off.

I think that you don't want the rootball to be limited to the old pot outline, so opening it up a bit gently (so a few shakes and a little digging around) and encouraging a bit of a spread of the roots is the best way to go.

You might incentivize the tree, you might kill the tree... I don't think that this is a good plan :)