Everyone on this thread seems overly concerned with "breaking cym roots" or "damaging cym roots".
Relax! It is virtually impossible to divide or repot a Cym without damaging or breaking roots and they will survive just fine. That is why I allow plants to dry out (lose most of the media moisture) before repotting as it is much easier to loosen the old media. I then remove with a sterile knife at least 1/2 to 2/3 of the root ball!!!
I then pick out the old mix with a pointed skewer, and remove any rotten (soft) roots from the base of the green bulbs. I know that in the south and south eastern states, it is necessary to treat the cuts with a fungal or antibacterial solution. However, in drier climates, allowing the plants to dry overnight will accomplish the same thing. Think of it as healing a cut on your finger - when exposed to air, a scab will form to seal the cut and the cut will heal faster.
Before you all start saying "Whoa Nellie" on this, let me give you my reasoning.
1) Roots are inevitably broken during repotting,
2) Broken roots will die at the break,
3) Leaving a bunch of broken roots, which will die and rot in the new mix, leaves no room into which the healthy roots can grow.
4) Roots will regenerate from above any cuts,
5) Keeping the roots above the bottom of the plant will help prevent rotting of roots in the initial reestablishment of the plant.
This has worked for me for more years than I want to admit.
CL