Pam et al, I don't know what the current rules are. Here is all that is stated on website when you go to select excursions:

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Request a Shore Excursion
You are making a request - this form indicates your interest in a tour, but does not guarantee tickets.
Requests are processed in the order they are received.
You will receive final confirmation of selected excursions in your cabin when you embark. All charges will be billed to your onboard portfolio.
Shore excursions listed as PREBOOK ONLY must be reserved through your travel agent or by calling 1-800-285-1835 (US/Canada). Prices for overnight tours are per-person based on double occupancy. Ask your reservation agent for single occupancy pricing.
Please note: Your request is being made on behalf of all guests in your suite. You will receive a faxable Shore Excursion Request Form within your documentation package; please do not complete and fax this form if you have requested your tours online. Booking on line is the preferable method as you receive a confirmation of your request. There is no confirmation received by faxing in the booking form .
Should you want to add to your choices simply submit another request, should you wish to cancel a choice please note that in the remarks section.
Children's discount pricing is available on some tours for children 12 and under and will be applied to ticket prices when your request has been approved.
We are unable to respond to questions regarding this request form.
You will receive a prompt acknowledgement sent by email to the email address in your "My Cruises" profile, listing all the excursions you requested. You may want to print a copy to take with you. However, be aware that if you have a spam-blocking filter on your email account, you might not receive the acknowledgement, but that it is not necessary to have it.

I know that LAST year any choice would override your previous choices. I am just trying to find out if that is STILL the way it works. Given that it doesn't mention it on the website, I think we need home office or recent cruiser's experience.