Trimming them back when you repot is good, especially if you break a lot of roots in the process. But this is a poor time of year to repot as the Jade is practically comatose. If you can, wait until spring. When you do repot, find a pot wider than tall (like an azalea pot) as the roots are only in the top of the soil. A deep pots means the roots are sitting on wet soil for just that much longer. After you repot, don't water for at least a week to allow broken roots to heal.
