Overrite parent functions using child functions

You can’t just redeclare the function in the child theme or call add_action a second time. It doesn’t replace it, it adds a second hook. As a result, you haven’t overriden it, you’ve duplicated the original. Child theme overrides only work for templates.

What’s more, by adding a second definition of wp_bootstrap_starter_custom_header_setup you’ve declared the function twice, which would generate a PHP fatal error. You can’t have 2 functions with the same name.

So first, we need to rename your function so that there’s valid PHP:

function sams_custom_header_setup() {

Next, add_action adds an action. It has no concept of replacing an action. If you call add_action 5 times, the function will run 5 times.

So lets add our action for the new setup:

add_action('after_setup_theme', 'sams_custom_header_setup' );

But remember, the original function got added too, so now both will run! So, remove the original:

remove_action( 'after_setup_theme', 'wp_bootstrap_starter_custom_header_setup' );

TLDR:

• You can’t “override” actions.
• But you can remove them and add a new action to replace them.
• Stop making multiple functions with the same name! That’s invalid PHP, it’ll break things
• Child themes let you override templates loaded via WP, not arbitrary PHP files, functions, hooks, etc

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Edit:

It seems the function in your parent theme uses apply_filters, you could just filter the parameters on the wp_bootstrap_starter_custom_header_args filter and modify the array itself. You don’t need to mess around replacing the function, or calling add_theme_support