Permanently disable Apple's OpenSSH?
The most simple way to disable the Apple provided sshd without removing or replacing it is just renaming it:

sudo mv /usr/sbin/sshd /usr/sbin/sshd.old


Additionally you may add a symbolic link at /usr/sbin/ to the /usr/local/sbin/sshd with

sudo ln -s /usr/local/sbin/sshd /usr/sbin/sshd