>Hmm. I wonder if anybody has tried to design a firearm that can be
>disassembled and reassembled to change the direction of ejection?
>(Compare with changing the direction the doors open on a refrigerator,
>although obviously far more challenging.)

While I don't know the actual mechanics involved, the Canadian variant of the M16, the C7 is made to have the ejection go left or right, making it rather notable among lefties.

Smith & Wesson's M&P series, among handguns, is supposed to be 'fully ambidextrous' but if that extends to where the brass goes, or if it is 'merely'(not so merely) the controls that can be rearranged for lefthanded shooters, I couldn't actually say.

...!
Gott's Leetle Feesh in Trousers!