I'm sorry I don't have an answer for your question, but in Tie Fighter you can also transfer energy between shields and lasers with the ; and ' keys (between L and enter).

Yes, you're right; but I used this only as example of what I need...

It's possible, but might not work as expected. Especially shift-somekey
combinations can be tricky due to how games read the state-keys.

Click on some key in the mapper, say "X", hit the add button, then push
some joystick button. Next click on another key, say "Y", hit add again,
push the same joystick button.
Test if pushing the joystick button produces "XY" or "YX" on the commandline.

Tried this already. The problem is that "X" or "Y" or both of them can have own commands, apart from "X+Y". In practice, such way cause to call either one of those separate commands, or even both simultaneously, while I want to have all three "X", "Y" and "X+Y" separately...

that "X" or "Y" or both of them can have own commands

It is impossible then.

It's a pity... Thank you for answering, anyway!

Not quite impossible. If you add joystick button 1 to the shift key and to the F9 key doesn't means you can't use F9 and shift normally too. I simply tried it and it works as Shift-F9 in my basic test.

Uh that depends on the app/game of course.
It is impossible to not have a keypress for f9 if you want to trigger shift-f9
as a combination. But i don't see any problem with the description of how
to bind multiple events i've posted anyways.