You can book the excursions now if they are available you can change up to 14 days prior to sailing if you choose
put the excursions in the cart online then I believe you may have to check out & submit a CC but the balance should be $0
some experts here have posted about adding the YWC excursions to get the discount
It may be easier for new pax to call & get someone at O do do it for you
less frustrating in the long run
JMO