Indeed, the topic linked to above explains how to redirect MIDI by channel and/or note range.
So you can do a keyboard split by assigning different note-ranges to two different instruments in the Renoise MIDI > input tab.
Once set up, you can save the configuration as a template song. This will restore the song (including your two instruments) the next time you start Renoise.
Another approach would be to use the Duplex Keyboard. Once configured then you can simply start Renoise and it will be ready to use.
But, if the desired configuration is not available out of the box (there are only a few different examples of keyboard splits) then… hmm, well, feel free to ask 