Hi,
I found an imcomplete sentence of an info i was looking for in the doc:
http://docs.pixologic.com/reference-guide/preferences/config/
It says:
“The master file is named ‘CustomUserInterface.cfg’ and resides in…”
I wanted to know where it resides and I have to guess where!
In fact on this other page I could find my answer: http://docs.pixologic.com/user-guide/customizing-zbrush/interface-layout/