Hi Leman
I know a seamstress(could dream about that mistress/ seamstress!) and got her to cut the arms about 6 inches from the shoulder. She put a gusset and velcro tie on also. Been like that for 2 seasons and standing up well. I wear a full length rashie under it during the cold of winter. Really happy with the outcome.
I had real problems with 2 previous winter suits being not flexible enough in the arms. Took me a while to work out it was not me being a 80 kg weakling but the wettie restricting my muscular frame

Now I am unsheathed and proud of it