I've recently bought second hand, but never flown, an aircraft, engine and JR X-378 controls.

The problem is this: I live in Japan, and bought this gear from an Australian who managed to get a special delivery (from the factory here) of the radio controls in the mode used in Australia, whatever that is, 1 or 2. None of the Japanese r/c flyers use this mode, and since I am going to need some help via a buddy box for a while, I need to convert back to the mode used in Japan.

What's involved? Does the Tx need to go back to the factory, or is it a simple matter of changing leads on the back of the controls sticks?

Any help would be appreciated.

It can be done, my advice is to get some help because you said you " never flown, an aircraft engine and JR X-378 controls"

You need to change the mode to mode 2 (I assume) in the "System Set-Up Mode"

Press and hold the 'down' and 'channel' buttons together, and turn the 378 on, then release the down and channel keys. Press the 'down' button until you get to 'stick',

Now press the + or – keys until you see 2.
Then press the 'down' and 'channel' buttons together again.

Turn off the transmitter, remove the crystal & battery, and open the transmitter case on the back, and change the ratchet and spring on the elevator stick to throttle stick.

Hope that helps, but please check with an experienced modeler!

Regards, Gert