If the soil is really bad and the tree is stressed. Combing out the roots a little bit and putting it in good soil might be a good idea. No root pruning should be done unless root rot is present.
As far as pruning junipers, you question would require several pages to address. For procumbens junipers, it is best to not cut the needle stems, they will brown, but eventually heal themselves. If you have shimpaku, scale like foliage, you can cut back in Spring. Then you might need to do a little pinching later in the season. However, pinching is more for finished trees. Even then, many people do not pinch or pinch very little. Young trees ot trees in trainign, should not be picnhed. Sometiems a tree is trained for 4-5 years plus before any pinching is done.
