The trouble with adjusting the shoulder is if you cut off that 1/2 inch you are actually making the armhole bigger. Before you do any cutting I'd run a basting stitch around the armhole taking out the excess and see how it fits.

You might be able to fix things by adding shoulder pads if they don't have them or a bit thicker ones if they do.

I thought about this some more----

If the shoulder pads don't work for you--leave the armhole alone you'll be opening a whole can of worms you won't like.

If you really have to rake the shoulders in, make a small 1/4 inch dart in the shoulder. It will make a much better job

Or you could take in the underarm seam a bit.

Thanks for your help. I think I will take in the underarm just a wee bit.