Those are the actions that would be performed:
mkdir /home/user/gentoo/lib.new
cp -a --reflink=auto -- /home/user/gentoo/lib/systemd /home/user/gentoo/lib/gentoo /home/user/gentoo/lib/modprobe.d /home/user/gentoo/lib.new/
mkdir /home/user/gentoo/usr/lib.new
cp -a --reflink=auto -- /home/user/gentoo/usr/lib/xml2Conf.sh /home/user/gentoo/usr/lib/Scrt1.o /home/user/gentoo/usr/lib/libffi /home/user/gentoo/usr/lib/python-exec /home/user/gentoo/usr/lib/gettext /home/user/gentoo/usr/lib/terminfo /home/user/gentoo/usr/lib/python3.7 /home/user/gentoo/usr/lib/systemd /home/user/gentoo/usr/lib/portage /home/user/gentoo/usr/lib/cmake /home/user/gentoo/usr/lib/Mcrt1.o /home/user/gentoo/usr/lib/gconv /home/user/gentoo/usr/lib/binutils /home/user/gentoo/usr/lib/debug /home/user/gentoo/usr/lib/perl5 /home/user/gentoo/usr/lib/gcc /home/user/gentoo/usr/lib/help2man /home/user/gentoo/usr/lib/gcrt1.o /home/user/gentoo/usr/lib/crtn.o /home/user/gentoo/usr/lib/crt1.o /home/user/gentoo/usr/lib/glibc-2.31 /home/user/gentoo/usr/lib/misc /home/user/gentoo/usr/lib/gawk /home/user/gentoo/usr/lib/tmpfiles.d /home/user/gentoo/usr/lib/pkgconfig /home/user/gentoo/usr/lib/audit /home/user/gentoo/usr/lib/crti.o /home/user/gentoo/usr/lib/engines-1.1 /home/user/gentoo/usr/lib.new/
mkdir /home/user/gentoo/usr/local/lib.new
ln -s -f -T lib.new /home/user/gentoo/lib
ln -s -f -T lib.new /home/user/gentoo/usr/lib
ln -s -f -T lib.new /home/user/gentoo/usr/local/lib