How to add custom function to a single blog without creating a child theme

Hi I hope you don't mind this share.

One problem that we solved was how to add custom functionality to individual blogs, without creating a different child theme for each blog.

This is useful is the tweaks are not big, but plugins (like Gravity Forms / WP-Leads etc) have filters that need a bit of tailoring. If all else it the same, it is a bit of overkill creating new child themes for each blog / site.

But with a simple bit of code in functions.php you can have individual 'add on' functions.php per blog.

/* do specific functions.php for specific blogs */
if ( is_multisite() && file_exists( get_stylesheet_directory() . '/blogs/'.get_current_blog_id().'/functions.php' ) ) {
		require( 'blogs/'.get_current_blog_id().'/functions.php' );

My technical notes blog explains this in a bit more detail and how you can do the same with CSS.

Hope it helps someone.