so for centos 7.5 containers my work flow would be to create a golden base image with workarounds and use that to launch centos 7.5 containers
create centos75-base container to add all workarounds then create/publish image centos7-systemdfix
# create a golden base centos 75 lxd container image to work off of
lxc profile set default security.syscalls.blacklist "keyctl errno 38"
lxc launch images:centos/7 centos75-base
lxc exec centos75-base -- echo "export LANG=en_US.UTF-8" >> /etc/profile.d/locale.sh
lxc exec centos75-base -- echo "export LANGUAGE=en_US.UTF-8" >> /etc/profile.d/locale.sh
lxc exec centos75-base -- source /etc/profile.d/locale.sh
lxc exec centos75-base -- sed -i "s|plugins=1|plugins=1\nexclude=\*.i386 \*.i586 \*.i686|" /etc/yum.conf
lxc exec centos75-base -- yum -y update
lxc exec centos75-base -- yum -y install wget openssh openssh-server curl curl-devel libcurl libcurl-devel
lxc exec centos75-base -- wget https://copr.fedorainfracloud.org/coprs/jsynacek/systemd-backports-for-centos-7/repo/epel-7/jsynacek-systemd-backports-for-centos-7-epel-7.repo -O /etc/yum.repos.d/jsynacek-systemd-centos-7.repo
lxc exec centos75-base -- yum -y update systemd
lxc exec centos75-base -- yum -y install openssh openssh-server
lxc exec centos75-base -- systemctl enable sshd
lxc exec centos75-base -- systemctl restart sshd
lxc exec centos75-base -- systemctl status sshd
lxc restart centos75-base
lxc publish centos75-base --alias centos7-systemdfix --force
lxc delete centos75-base --force
use centos7-systemdfix image to create container centos75
lxc launch centos7-systemdfix centos75
lxc config set centos75 boot.autostart true
lxc exec centos75 -- systemctl --version
systemd 234
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN default-hierarchy=hybrid
edit: may have some issues with updated systemd 234 though Centos 7.5 container operation not permitted?