Silly question.

Regarding making our own pre-patcher, how exactly can we know if Nexon has modified the patch content? Do we check the FTP every hour? Even if we did check, how exactly do I notice this change?

If they remove/add some KBs of content, it'll be obvious, but what if it's the same?

Just check the FTP and see if the size of the file has changed at all. The chance of them changing something and the file being the exact same size in bytes is pretty low.