Following up on what I did... I put my OP #.

After speaking with the cruise agent, I found out that the United Cruises agency does not validate the MP# at the time of booking. They only submit it for credit after the cruise completes. Since my current OP # will be my future MP # at that time, I feel comfortable that this will work. The agent also say that I can call in and change the MP # at any time until it posts.