Yes Beth, that does work - as long as the excursions aren't in a 'wait-list' status. If you cancel on board and there's a wait-list, you go to the bottom of the list. But we were able to use our OBC on Regent after checking that the excursion was available for booking, and they were quite happy to cancel our original booking, crediting it back to our credit card, and using our OBC to re-book.
