I may have, although I don't use that method. In my book, I give a list of options where I think things would be handy after each customization and let the user decide.
I don't think I currently have FX/DX programmed on the Z8. I'm hot and cold on that feature TBH. I sometimes hit it accidentally and end up shooting the wrong format for a bit until I realize it. If I was going to use it, I'd want it on a "safe" button like the WB button or - the video record button

(Although, I
personally think the video record button is ideal for cycling AF, but to each their own)