Take it to a men's tailor and get their opinion.

OP here... thanks for the advice. I'll ask the tailor first and decide!

A jacket's shoulders are next to impossible to alter well -- if those don't fit, you pretty much have to take apart and rework the entire garment.

2-3 sizes in something structured like a blazer might not be alterable. It would have to be totally taken apart and reconstructed, likely losing the integrity of the blazer. I’d pass it on

Do you love it? It sounds like you might. If so, do what it takes to wear it. If not, pass it along. Envision how you will feel when you see your friend wearing it. Happy for her, or jealous and kicking yourself?

If you have a good tailor, she will be honest if she is able to alter it. My tailor has told me on a few occasions that she could not tailor what I brought.

My sister passed me her Balenciaga blazer, but it is 2-3 sizes too big for me. Is it worth it to have it altered (in the shoulders mostly and some width)? Will a tailor mess it up? Wondering if it's worth the cost to have it altered, or just give it to a friend who can wear it. The blazer is beautiful though, and in new condition. I have a tailor I like, but I've never given her a blazer to alter.

Thank you dcurbanmom.