If you just want to place it in a new pot and add soil, you can certainly di this now. If yu would like to do more extensive root work on it, my idea would be to either do it now (If you are in temperate climate, northern hemisphere) as most plants will make a last growing spurt in august / september before settling in for winter: The roots are now balanced to the canopy, and if the plant is healthy it should recover easily. Otherwise, I would wait untill earlie spring befor new growth appears.