rp_addon_category

This filter is applied to use the addon category of child addon, it is including one parameter.
$addon_category_args -> is an array containing addons category.

An example of how you can append is below:

function add__addon_category( $addon_category_args ) {
$addon_category_args = //passes arguments on this array.
return $addon_category_args;
}
add_filter( 'rp_addon_category', 'add__addon_category', 10, 1 );