I've researched this before. There are no procedures for shoulder reduction, or surgeons crazy enough to carry out the operation for that matter. It's a part of the body designed to bare intense loads, and is a major part of the skeletal system. Anyone who got their shoulders surgically reduced would probably never recover from it either as far as I can tell. Hormones can reduce muscle mass in that area which can make them look smaller and in some cases where the muscles are really big, pull the bones close together... Probably not by a lot though.
As for your neck, that's probably all muscle, in which case hormones should affect it too. I've never heard of anyone having a thick neck because of their spine being too wide. But, don't just rely on hormones though. If you adjust your diet and reduce your protein intake, that could reduce muscle as well.
Hope this helps!