I’m currently a 12N in the Reserves; I’m also thinking about reclassifying to 11B. Would I need to go through BCT again?

No once you go through basic you don't have to go through it again unless your airfoce navy or coastguard tryi g to join the army or marines a marine won't have to go through basic if that individual wants to join any other branch and that goes for army to unless he or she wants to join the marines but for changing MOS you just go to reclas school

You shouldn’t need to go back to BCT, but you would most likely cycle in toward the end of a OSUT cycle or be sent to a 10 level certification course. Also be aware there are not that many 11B positions in the reserves as compared to most state’s National Guard. You may be better off looking to the NG if you are interested in Infantry. Good luck!

You shouldn't have to go thru BCT again, but you may end up joining the training company at the tail end of their BCT before AIT starts, being they are OSUT. That happened to me when I reclassed to 12B.

i believe you must be out of the service for more than 5 years or if you decide to go into the Marines, you must go to marine basic as they do not recognize any other service basic training

As most have said, no you will not have to attend BT, but think about your future. 11B has very few positions in the Reserves. The promotion opportunities wil be small. I would recommend Civil Affairs.