This is an opinion only and has no written guidance to back it up:
Submarine duty is strictly voluntary. If you've never been assigned to a submarine, I would think you could change your status.
Definitely call the detailers. If nothing else, I would think it would help them plan ahead because there are different detailers for sub and surface.
And to build on the previous post, whether or not you have already submitted your 1306, duty preference/dream sheet, prepare a new form and send your updated preferences to the detailers immediately.
EDIT: added more after search for info
If you want something in the Navy, I recommend you become familiar with the governing doccuments, which for your case I have found on the Internet (Google):
MILPERMAN 1220-040
NAVPERS 15909G
COMNAVCRUITCOMINST 1130.8F
OPNAVINST 5355.3B
As with anything else in the Navy Nuclear Propulsion Program, accepting, "That's the way it is because I said so" is not good, even when learning about the propulsion plant.
Know the source documents and written requirements. (You might be surprised.)
P.S. You might think I'm wasting your time because most of what is said in those articles (1) doesn't have anything to do with what you want, (2) refer to each other in a circular fashion, and (3) repeat and restate the same things that the others state. However, you just might find what you want buried in there. Also look for NOTES which are like updates. I can't help you with finding the applicable notes (I used to look through binders in the yeoman's office), but they will usually have the same number as the governing document (e.g. NAVPERSNOTE 1220.040 ... I have made this number up just for example) and a revision (capital letter)) and a date ("dtd Sept 1982"). Also make sure that you have the current revision.