Dan: For some reason, clefs cannot be reached by pressing Shift+Tab, although Tab
will select them. As far as I am aware, these are the only staff items which
cannot be reached by Shift+Tab. (Instrument changes and key signatures on
one staff work as you'd expect.)

Tim: I've just tried this myself and you should be able to locate the clef using
the tab key.  This is what happened:

1 - I navigated to bar 4 and created a bass clef;

2 - When moving through the score with Tab/Shift+Tab, I get a notification
at bar 3 that tells me that there's a bass clef at the end of the bar;

3 - When I tab/shift+tab to bar 4 I get told the voice number and the
presence of the bass clef.  Pressing Q at this point allows me to change the
clef, or I could just press Delete to remove it.