Unable to customize resolv.conf

I'm trying to customize resolv.conf but no success so far.
I want to run unbound listening on localhost only and use customized hostname.

I've been able to customize name in the web interface (easy)
I changed cloud.cfg then changes hostname and hosts accordingly.

This works

then I also changed dhclient.cfg with supersede domain-name-servers and supersede domain-name but this doesn't work and resolv.conf is always erased with default value.
I even edited interfaces to add dns-search and dns-nameservers

I suppose my mistake is with dhclient.conf but I can't figure out what's wrong and on-line documentation doesn't help.

Any idea?

TIA