Just for closure, I have completed my modification of the CLS2000 head. I purchased a complete set of dichroic and UV filters for the head at $200. This gives me some spares just in case. I put the magenta filter in the slot for the supplementary holder. Now split grading is as easy as can be. Now I dial in my starting filtration with yellow and magenta (somewhere between grade 0 and 2), make my soft exposure, set the white light lever to remove the filters from the light path, set the supplementary filter into the light path, and make my hard exposure. Amazingly easier and faster than repeatedly dialing in the filter values. Thanks to all for your advice and comments with this.