My wife is a fit designer for apparel, I wish she was on the board to help you. I can only say the little I know about fits (I'm a fabric guy). Chest and stomach type adjustments shouldn't be too difficult as I believe it would just require some seam busting and re-sewing, same with armholes.

The main issue I see is back length due to the back pockets, elastic and/or sticky band, etc all potentially going on back there, and if it's full zip, having to take it up in the front could be an issue without maybe replacing the zipper.

I'm no expert on construction, but those are the things that pop in my head.

The Assos/BMC jersey I just got (for FREE! WOOHOO!), is an XL, so it's a little big, I may have her take a look at it and get her feedback on altering. If you want, I'll try to update the thread, if you think it'd be valuable to you.