I can access files inside a LXD container by running lxc from the host:
root@Host# lxc exec Container_Name bash
root@Container_Name# touch /tmp/hello
Or by accessing the files directly from the host under /var/lib/lxd/containers/Container_Name/rootfs:
root@Host# touch /var/lib/lxd/containers/Container_Name/rootfs/tmp/hello
Is there a preferred way?