As some have read, I am looking to buy an '08 Patriot Sport 4x4, Sport E package with 5 speed. They come stock with the 120amp alternator.

Problem is that the you cannot get the 140 amp alternator unless you go with the FDII CVT off road package. There is no way to get the 140 amp alternator with the 5 speed.

That said, how easy is it to get a stock 140 amp unit at a later time and swap it?

Since the Patriot shares the same alternator as the Compass and possibly the Dodge Caliber, I think you will see many after-market alternators coming out, in addition to replacements for the original 120 and 140A ones.