While it's easy to change each emu's inputs, if you keep updating it can be
a PITA repetitive. (One of the reasons I stopped releasing my own version of mame.

) I understand the set and forget (even though I upgrade regularly) mentality. Plus from the coding point of view I'm sort interested in what's going on: the numbers have to come from
somewhere.
Very quick skim of the source, looks like the windows version up, down, left, right (200,208,203,205) are VB/VC scancode numbers for the arrow keys, and the other OS compiles use different numbers for the direction buttons. OTOH, all OS compiles use the same key numbers for the other inputs. Too many different "scancode"s on google, hmm...
It
almost looks like keynumber+1. Err, like from
the table on this page (plus one). I think that would result in capslock, a, s, leftshift, z, x, slash and backslash? (Easier for me just to download and test zsnes inputs... Nahhh, not at work.

)
As others said, it's easier to remap in the emu, save the remapped inputs file somewhere, and just copy it to the new folder when you upgrade.
But if you want to do it your way, keep posting on what you find; I'll see it I can help even if others keep telling you to do it differently.
