Ah, thanks for the details. The -S part is the second point in comment 2. It seems to me that /lib/udev/rules.d/85-hdparm.rules already applies *all* the settings (i. e. including -S) from hdparm.conf, so that should work on at least boot and probably also hibernate.
So I'll modify this to be more closely to your original proposal.
Ah, thanks for the details. The -S part is the second point in comment 2. It seems to me that /lib/udev/ rules.d/ 85-hdparm. rules already applies *all* the settings (i. e. including -S) from hdparm.conf, so that should work on at least boot and probably also hibernate.
So I'll modify this to be more closely to your original proposal.