No. The Main PART is always MAIN, the Layer PART is always LAYER, and the SPLIT Part is always SPLIT.

Ok, too bad but thanks.
Is it perhaps possible by connecting a midi cable from out to in on the CP4 itself? Tnx!

Sorry, I cannot recommend connecting the MIDI OUT to the MIDI IN for any serious musical purpose. It is just wrong on so many levels. What is it you are really trying to accomplish? Start with an understanding that the Main Part is always active, the Layer Part matches the range of the Main Part, and when you add the Split Part it becomes the left hand sound, while the Main and Layer become the right hand Part. It is not an overlapping situation, it's a lower/upper situation. A single Split Point is defined.

If you "sometimes need more than 2 Layers" you should use the MIDI OUT to connect to a second sound module. That would be the proper use of the MIDI OUT function. In fact, in the design concept, you can control as many as four external Zones using the Master Keyboard function. The correct solution would be to add an additional synth to the end of the MIDI jack. The elegant Master Keyboard function will allow to integrate your external device into your CP4 Stage setup, as you require. The Master Keyboard function is designed to control external devices.