@Vox I don't think an experienced leather worker would willingly alter aged leather. It would be a better option to have a new coat made in the same style and you wear it in.
What makes the coat special is your father. You could similarly make your own coat special. If cared for properly, it will likely be the last one you would need.
@Vox It can be done but it's worn in leather. Density changes as the leather stretches until it is broken in.
@AmpBenzScientist
Huh. I hadn't thought of that. I just recently had a pair of my husband's cayman leather western boots restored and repaired, including a rip in the upper. They did a fantastic job. Made a $1500 pair of boots look like new for about $200. I didn't realize cutting down this coat would be much different in terms of skill needed, although I figured it would cost more. (Dad had 5 inches and 150 lbs on me). Maybe I'll just move the buttons and add a belt...?