Can I siege/take county that is under the control of a revolt?

So Norway is defending itself from an internal revolt that has taken over several provinces including Cornwall. I have a De Jure claim on it, but it is currently taken over by the revolt (when I click on the county, the revolt coat of arms is shown in between the castle/city/bishopric ones - and it has the usual striped colours on the map).

So my question is (because I am playing Ironman, don't want to risk doing something stupid):

Can I declare war on Norway for Cornwall and actually siege and take it, or will the game only allow me to do that once the revolt is crushed?