AFAIK you should use a bind mount to do that. I suggest trying with the following mount unit:
# /etc/systemd/system/var-lib-snapd.mount
[Unit]
Description=bind mount snapd from /home to /var/lib/snapd
[Mount]
What=/home/snapd
Where=/var/lib/snapd
Options=bind
[Install]
WantedBy=multi-user.target
RequiredBy=snapd.service
Save it to /etc/systemd/system/var-lib-snapd.mount
, then:
# remove the symlink
$ rm -f /var/lib/snapd` symlink
$ systemctl daemon-reload
# enable the mount unit
$ systemctl enable var-lib-snapd.mount
and lastly reboot.
@zyga-snapd may also have some suggestions here.