PacAce wrote in post #3828096
In case it wasn't obvious from the other posts, you can't directly assign the "*" to focusing on the 40D like you can with the previous models via C.Fn-04 because the AF-ON button was set up specifically for that purpose. But, what you can do is swap the functions of the "*" and the AF-ON buttons so that you still use the "*" for focusing, instead of the AF-ON button, on the 40D if you've gotten using to use the "*" button.
In case it wasn't obvious from the other posts, you can't directly assign the "*" to focusing on the 40D like you can with the previous models via C.Fn-04 because the AF-ON button was set up specifically for that purpose. But, what you can do is swap the functions of the "*" and the AF-ON buttons so that you still use the "*" for focusing, instead of the AF-ON button, on the 40D if you've gotten using to use the "*" button.
I did it. And I like it.
The main reason to do this is to have "*" for focusing because battery grip doesn't have AF-ON button. So setting "*" to focus gives me same behavior with the grip. And AF-ON gives an exposure lock which I didn't have with 20D. That's nice.
The only issue is that in this setup I have to press AF-ON to Zoom-Out while browsing through pictures on the card. And pressing "*" is switching camera into shooting mode and focususing.
I would like to swap AF-ON and "*" for shooting only but not for images playback. 
