A CBBC extra type of thing as the down time loop from 9pm-7am? Would the trust accept that as a useful use of the time?
Back in the old days when Freeview had BBC Red Button on 301 and 302 the CBBC Extra stream would appear there when there was nothing else to show on it. This had the effect of CBBC Extra occasionally spending more time on air on 301 than the channel (then on 30, later 70, later whatever it's on now) it was being an extra to.
However I very much doubt 9pm-7am would get the Extra loop; if you're going to do that you may as well just extend CBBC to a 24hr service and have done with it.
Has the CBBC brand been rolled out internationally at all or is it just CBeebies?
Though many CBBC shows do air abroad (those made in house by/for the BBC I should say, rather than those made in conjunction with other broadcasters), the CBBC brand is probably only limited in that regard to end-caps.
Sign of a good brand when you can spin it off across the globe with considerable success. I take it CBeebies internationally has similar presentation to the UK channel?