Set backorder default to “notify”

Hi guys,

I am trying to change the default setting for allowing backorders. There are the options, yes, notify and no (which is default).

I want to change it so notify is the default setting, so newly created products have it preconfigured.

We need this, because there is no bulk editing for this value for variable products and most of them should be set to backorders: notify.

I tried the following in my functions.php, but there is no change:
First try:

add_filter( 'woocommerce_product_backorders_allowed', 'notify_default' );
function notify_default( $default ) {
	$default = 'notify';
	return $default;
}

Second try:

add_filter( 'woocommerce_product_backorders_allowed', '__return_true' );
add_filter( 'woocommerce_product_backorders_require_notification', '__return_true' );

Any ideas what I did wrong. Am I even going in the right direction?