You can do what you want to do with the Order directive, but without adding the additional invalid/conflicting htaccess code. You cannot do a check for a mistake in the htaccess code with the htaccess code.
# Blacklist hackers and spammers etc. Order Allow,Deny Deny from x.x.x.x Deny from y.y.y.y Deny from z.z.z.z Allow from all