You can get root ssh on the device relatively easily by remounting the filesystem read-write and modifying /etc/ssh/sshd_config to point to your keys.

Placing something like the following in `/autorun/95-enable-ssh.sh` on the SD card should work, making sure to modify the `echo "your keys"` line.
<code bash>
#!/bin/sh

mount -o remount,rw /

echo "Port 22" > /etc/ssh/sshd_config
echo "PermitRootLogin yes" >> /etc/ssh/sshd_config
echo "PubkeyAuthentication yes" >> /etc/ssh/sshd_config
echo "AuthorizedKeysFile .ssh/authorized_keys" >> /etc/ssh/sshd_config

mkdir -p /root/.ssh
echo "your keys" > /root/.ssh/authorized_keys
chmod  0700 /root/.ssh

systemctl enable --now sshd.socket

mount -o remount,ro /
</code>