Can suit jackets be made larger?

Suit alterations are actually quite simple, once you understand the basic theory. The first thing you need to know is that a garment can only be altered on a seam. You can either “take-in” a seam (make it smaller) or “let-out” a seam (make it larger). “Taking-in” means making the garment smaller.

Can a tailor change the size of a jacket?

The waist can be nipped, the length can be taken up (although even that is a big job that most tailors will discourage because it affects where the pockets sit), but the shoulders can’t be changed without taking the whole thing apart, an exercise that might cost you more than your money-saving coat did.