Yes you can, but I wouldn't do it on my own... specially if you want to change to external gear mech.
I own both a Raven Tour and a Catalyst. In this case I don't need to change anything from the hub... just swap the tires and away I go! But often I've thought about changing the axel plate in order to use it in a nice frame, disc ready, that's collecting dust in the garage cause it has convencional gears... but of course this is an easy thing to do.
Anyway, Rohloff hub is really well thought and you can change almost everything.