Add snippets for other php files like pluggable.php

Hi, is there a way to use this to add code snippets to a file other than functions.php? I want to add a snippet to pluggable.php having to do with the password generator. If I can’t do this with this plugin, do you have any suggestions? It would be cool to be able to specify what file you want to add the snippet to.

Thanks,
Aimee

PS. I’m not a developer, so if this is a stupid question and there is like a way more obvious way to accomplish this, that’s great too.