I want to execute my own welcome new user email notification instead of `function welcome_user_msg_filter(){}` located in ms-functions.php

I recently [learned how to override functions in pluggable.php](https://wordpress.stackexchange.com/questions/56571/how-to-override-a-pluggable-function), but the function I am referencing does not have its own `if ( ! function_exists( 'welcome_user_msg_filter' ) ) {} `.

Has anyone ever overridden a function that lives in `ms-functions.php`?

If so, how do you go about it?

Thanks