Here is my solution to access 6 flight modes on Graupner MZ24 transmitter.

As described in ColinBouriquet's blog, also two swithes has to be activated on MZ24 to manage 6 modes.

The idea is to make the tx send the following to the receiver to activate the 6 modes:

Mode 1:  PWM: 0-1230

Mode 2:  PWM: 1231 - 1360

Mode 3:  PWM: 1361 - 1490

Mode 4:  PWM: 1491 - 1620

Mode 5:  PWM: 1621 - 1749

Mode 6:  PWM: 1750 -

1. Activare Base
   1. Activate Channel set
      
   2. Push # 5. Aux 1 (the channel which controls the modes) 
      You will then see the Select - No - Clr picture
   3. Activate the chose switch. I have used  Sw 5
      On the left top of the tx.
      Initially, the tx will send these PWMs to the receiver:
      Switch far back: 1165
      
      Switch miiddle: 1504
      Switch forward: 1817
      
2. Activate Base again
   1. Activate Channel set
      1. Activate SW7 to channel 9
3. Activate Function
   1. Activate Prog mix
      1. Mix Channel 9 to Channel 5
         
      2. Hit the >> button.
      3. Adjust the mixing image like this
         
4. The movement of the switches will then give this result
   

You the can access all 6 modes.. Now go to Mission planner an allocate the your chosen modes to the 6 modes you created.