Every radio I've seen has been switchable by swapping a couple of parts and either a software setting or moving a wire connection inside the transmitter. (that's so mixing functions move to the other stick as well). There might be exceptions though.

There are Mode I flyers in the US (even a few on the boards here), but they aren't common, most US gear is Mode II.

(side note, there is also a Mode III (well, sort of). Same as Mode II, but swap the ailerons and rudder, so throttle is on the left with ailerons, and elevator and rudder on the right. But it's extremely rare, but you can use an unmodificed Mode II TX that way).