There are posts in the forums for other cruise lines where this has been allowed. But it is only allowed when it is approved in advance. And the advice is always to get it in writing and bring that along with you to the ship.
Without this being taken care of in advance, there will be problems with immigration as that will not be set up in advance. Also, be aware of the fact that a port can always be missed due to weather. And one last thing, do not expect any return of any part of your cruise fare because you did not do the entire cruise.