Goto scheme editor and type the amount of fall damage you want here:

As you see in the picture, max is 254. Pick a number less than that or so. Some of the value are not defined in the game, so scheme editor just gives you the nearest value possible.
To edit your scheme file, choose your file from your system, click on "load", then change its fall damage value, then click on 'save this scheme to my inbox". you can download it right after that.