Repotting in winter

Is it possible to repot bonsai during early winter? I have a bonsai on the brink of death and I want to revive it. It currently uses water-retaining soil (I understand this is a no-no) so I bought some proper bonsai soil for them in spring. Is it okay to do it now?

Normally you would not repot a tree in winter.

You have a sick tree. Repotting is rarely an answer. If the tree was doing well in the current soil before, it is not the soil per se that is causing the trouble.

First find out why the plant is not doing well. After that consider which actions are appropriate. Just repotting because it is water retaining soild makes no sense. Better to adjust your watering.

I was looking at the roots earlier and they were a light brown but not mush or anything.