Dear Uladzimir and Henning,

First of all thanks for your answers.

I confirm that I did not found a straight forward way to do it. After all,
it is not necessary also. Mainly because two reasons: 1. debian packages
dependencies are sane and do not require any bypass; 2. the dpkg database
is left with a unsatisfied dependency and this get bothering forever.

Unfortunately, it is about a thirty party proprietary deb packages source.

I am testing a fake .deb in which the postinst unpack the target .deb and
it uses install to deploy the content in the rootfs. I hate to use this
trick but I need just one file from that package.

In brief, it does such a thing:

set the resolv.conf
apt update
apt download
dpkg -x
install
rm all

Every suggestion will be appreciated.

Best regards, R-