You need to set your quality profile cutoff lower if you don’t want it to upgrade. If you want it to only stop after its been watched then you’ll need to use a script like @lordlynx suggested.
Propers will only download within a short window (offhand a couple days), not months later.
We don’t plan to add an option like you suggested, but have talked about ways we can get the watched status and use that the aid decision making.