Their excursions don't change much from year to year. After you make final payment, Princess will send your TA your pre-cruise information, which will have a current excursion book in it.
the excursion information on their web site is very helpful, you can download a brochure or you can get one from your TA. About the only major change from year to year would be in price. You can reserve your excursion 60 days prior to sailing on line or have your TA do it.