Help with ModMerge/chitin.key on Mac

Hey guys, long-time player first-time mod user here. I'm a total noob when it comes to this stuff ...

I've converted modmerge to an exe. and placed it alongside the chitin.key however I get the "no such file or directory" error message when I try to run it in Terminal, I'm guessing this is because chitin.key is listed as a Keynote file.
How can I change it to something modmerge will recognise?
Thanks in advance, can't wait to get stuck into some of these mods!