I want to add a single line to Twenty-Eleven's functions.php file, to allow my site to use the Page Navi plugin.
It's easy enough to add the line to the existing theme file, but that pretty much makes future theme updates not-so-smooth, as I will need to remember to go in and add the line again.
I am able to override theme CSS with an external CSS file via the Custom CSS plugin. By keeping the custom CSS in a separate file, it isn't affected by theme updates. Is there a way to do a similar thing with a PHP file, without having to resort to a child theme?