get the source, copy not_tetris_2.love (or whatever) to not_tetris_2.zip
extract that into an existing folder.
Edit the main.lua file, the love.keypressed function starts at line 751 I think.
You could use geany. Set execute command as
and press F5 if you want to test.
EDIT : ok actually i think you'll have to look at gameBmulti.lua instead. main.lua only takes keypresses for menus.
Man does not tetris's code look 10x cleaner and shorter than mari0's.