Shortening should be no problem. I alway urge our customers to have the sleeves on outer coats about 1/4" longer than usual. This allows the sleeves to be shorted down the road when the inevitable wear on the sleeve ends comes to pass.
Winston Tailors www.chipp2.com
. . . might be if there's a cuff belt or button tab to close up the sleeve, depending on how much one intends to shorten. Moving those would definitely leave holes, or at least marks, which would be very difficult to minimize in the type of heavy fabrics involved. Well, maybe not so much for a pea, which is rougher. At any rate, that would add to the cost if it were necessary.
Shortening is not so much a problem otherwise as lengthening. Even if the coat were not previously worn, the cuff fold is very likely to leave its mark in a line around the sleeve where it was formerly located. Can be hard to erase.