Yes, you can go onto the credit card website, sign in and apply the points to the reservation however you like (towards cruise, OBC etc.). I would just make sure you do it sooner rather than later as it can take several weeks. Also, I would alert your TA so they can keep an eye out for it. I just did this and as final payment approached had to call RCCL with TA to have them make sure it was credited as it wasn't showing on the TA website.