"Tania Replacer" is the solution for my geometry problem. Because the originale twi'lek female head skinning is a bit different, so I excluded some vertices from the neck base from the head envellope.
But, in case of a new model (not a replacement with a new name & texture), like me, you also need to hex edit the mdl file for changing the texture name, the tool seems to inject the texture name from the old .mdl.
Thanks again for the proxies tricks ! It save my life !