Hi Cem:
There is no direct way to send keys from a keyboard to the quadstick and use them like a sip or puff hole. It can be done with voice commands.
Increment and decrement mode both wrap-around, so if you decrement several times, you can get to any mode. For instance, in the default configuration, if you decrement_mode while in mode 1, you will end up in mode 6. The same is true for increment_mode, if you increment the mode while in mode 6, it will wrap-around to mode 1.
Increment and decrement mode can be activated by any sip/puff tube. If you cannot use the side tube, you can use tubes on the mouthpiece. There is an example of a configuration that does not use the side tube: