Your approach only works for nodes sending the string 'Bitcoin XT'. XT nodes are currently relaying the exact same information so there's no point in block them until January 2016.
I appreciate the mention.
Code:
# chmod 755
I appreciate the mention.
chmod 755 does for some reason often feel like the answer to everything
No, chmod 777 is a much more powerful solution to permissioning issues.
Both are inadvisable in a root account/Mandatory Access Control system, chmod 777 in particular; the 3rd '7' will make the file or directory readable, writable and executable for Others. Other is the most sensitive access level, that's the rest of the internet that can address your IP.