echo "sshalt nnnn">>/private/etc/services
(editing the file directly seems to crash every time) -- The letter n in the command above, indicates a digit of the alternate port of your choice.
Edit: Btw, make sure you use BOTH of the carrots in the echo command! >> is good. > is well, you just hosed an important system file.
Use the gTxtEdit app to edit /Library/LaunchDaemons/com.openssh.sshd.plist
Look for SockServiceName and change it's string to sshalt:
Save the file, reboot and enjoy!