How can I create a hook into an external module I want to be able to alter a function inside another module like a hook, but I'm not sure if that's what it's called. I want to alter a function inside another module from my module without changing the external modules code.

This is in version 7.x.

Thanks
Frank N.
PHP offers no mechanism to do that.

If the external function isn't a hook (i.e. it doesn't use module_invoke() or drupal_alter() to gather data from other modules) then the only thing you can do is patch the function in the external file.