Thank you all for the replies! Overall it seems that itineraries do change, but there needs to be a reason for it (for example bad weather). Seems that experiences with actual changes varies.
Thanks for the advice to check or discuss with the tour operator to refund. They normally not refund but they will see that in case anything changes if they have availability on a different day. I guess it is a gamble for this one port that I am going to take... @davekathy, the ports are St Kitts, Barbados, Martinique, St Lucia, Antigua. Are there any ports more difficult with hurricane season/ bad weather?