It has been some years and I'm not actively using this so I could have some misconceptions at this point, but I do not believe the header_filter_rules will leverage the @list notation that the _these_nonmembers does.
The use case being the administrator of list x needs everyone on list y to be able to send to list x unmoderated. However, they do not moderate list y and do not have knowledge of who is on list y. Therefore they cannot know if any of list x members should be unmoderated nor would they know who the put in the header_filter_rules.
It has been some years and I'm not actively using this so I could have some misconceptions at this point, but I do not believe the header_filter_rules will leverage the @list notation that the _these_nonmembers does.
The use case being the administrator of list x needs everyone on list y to be able to send to list x unmoderated. However, they do not moderate list y and do not have knowledge of who is on list y. Therefore they cannot know if any of list x members should be unmoderated nor would they know who the put in the header_ filter_ rules.