It really depends on what plants you're talking about and where that particular plant is in its growth cycle. IOW, you wouldn't want to buy a deciduous tree right now, bare root it, and put it in a different soil, but that would be a perfectly fine undertaking in spring.

There can be significant problems that develop from using two soils in the same container that are very different because of their differences in water-holding abilities, so I always try to bare root the woody material and plant so all the soil is homogeneous as soon as is reasonable. For smaller plants/bedding plants/cell pack plants, I usually just tear off the bottom of the root mass & work my fingers up into the remaining roots, then pot into the new soil & call it good. Larger plants all get bare-rooted if they aren't herbaceous (as opposed to woody) material. I never take any great pains to be gentle with roots, and the plants don't seem to mind, but remember that timing can be a factor. Most of the potting/repotting I do is in the spring when young plants are bursting with energy and extremely resilient.

Al

thanks Al

andy