When accessing iNotes on a Domino 9.0.1 server from a Blackberry 10 only Full mode is available and that's pretty much unusable.
From the Blackberry Browser you can select Personal Options on the redirector page and select Ultra-light mode, but that generates a browser error "This webpage could not be opened. There are too many redirects".
After going into iNotes in Full Mode on the Blackberry browser the dropdown at the top right show Full Mode under the user name but no option to switch to ultralite.
Using iNotes from a browser on a computer you can switch back and forth between full and ultra-light with no problem. The issue seems specific to the Blackberry browser.