Savedconfig

savedconfig is Article description::a USE flag that, in general, preserves the saved configuration files upon package updates. It allows for the updating of other files from a package update while, at the same time, guaranteeing no changes will be made to some specific files.

Usage
Setting  on a per-package basis will restore the configuration files from the  directory. Make sure the USE flags allow for appropriate dependencies.

External resources
https://packages.gentoo.org/useflags/savedconfig - An online view of packages containing the  USE flag.