The first couple of times I tried enabling customization it didn't work either. I was sort of suprised, because I'm usually pretty good with things like that. I found the procedure simple to understand; it just didn't work when I (as far as I know) followed the directions exactly. I'd say keep trying it, and you'll probably get it.
One tip that may or may not help is to actually count the 20 clicks. I know the directions say that you don't have to count them, as the light will stop turning off after the twentieth, but on one of my attempts (where I wasn't counting), the light stop turning off but I kept on clicking before noticing, and the command failed. Maybe I did something wrong, but it might help to count exactly 20 clicks and then do a press-hold.
One tip that may or may not help is to actually count the 20 clicks. I know the directions say that you don't have to count them, as the light will stop turning off after the twentieth, but on one of my attempts (where I wasn't counting), the light stop turning off but I kept on clicking before noticing, and the command failed. Maybe I did something wrong, but it might help to count exactly 20 clicks and then do a press-hold.