Reply to 1 CDJ400 to control 2 decks in traktor in MIDI mode

i wanted to ask whether it is possible to use 1 CDJ400 in MIDI mode to control 2 decks (i.e. A and B). i read that in cdj400 you can select different midi channels and i want to know whether you can have a keyboard shortcut to switch the channel and control different decks with 1 cdj400. or even to change the channel from the device itself when playing live.
thanx