Overriding an Array in a Plugin’s Class/Function from functions.php

OK, so you’re trying to create your own class that is extending the class from plugin. The problem is that the plugin won’t use your class, so you’d have to modify the plugin.

On the other hand, if you take a closer look at that class:

    public function display_meta_box($post)
    {
        $requirements = []; //Array I want to change with my own

        $requirements = apply_filters('my_checklist_requirement_list', $requirements, $post) // . <--- Array I want to change with my own
    }

you’ll see, that there is my_checklist_requirement_list filter in there and you can use it.

So all you need to do is to put this in your functions.php:

add_filter( 'my_checklist_requirement_list', function( $requirements, $post ) {
    $requirements = array( ... );
    return $requirements;
}, 10, 2 );