Comment 9 for bug 651438

The issue is that %_netsharedpath as currently implemented doesn't work
"after the fact". In order to function as expected, %_netsharedpath needs to be
in effect when the package is first installed. This way the "skipnetshared"
state gets recorded into rpmdb and erasure (on upgrade or otherwise) knows to
leave it alone.

Getting %_netsharedpath defined for initial install in anaconda might be tricky/impossible, I dont remember the exact details of what can be done in kickstart %pre. It should be possible to work around it later with something like

# echo "%_netsharedpath /usr/local:/var/spool/mail" > /etc/rpm/macros.netshared
# rpm -e --justdb --nodeps filesystem
# rpm -Uvh /path/to/filesystem.rpm