I'm not exactly sure what you are asking, but it's worth knowing what a tailor can and can't do. Sleeves and pant legs can be shortened without a problem, and sometimes lengthened a bit if there is extra fabric. Jackets and pants can be slimmed down. Making shoulders smaller will require re-cutting the jacket and is likely not worth it. I don't think anyone can make the shoulders bigger. Shortening a jacket can be done, but proceed with caution.
This is exactly what i wanted to know.
(1) One cannot increase shoulder size,
(2) If shortening a jacket, do it very carefully.
I asked because there's often some superb suits/ SCs here that I would consider buying but they're a size too large or small.