I'd say as long as they don't have any refresh-reducing powers, they are still a "pure mortal." Once they start getting some refresh-subtracting things (other than mortal stunts) then that's some sort of supernatural jazz taking wrapping it's mojo up into them, and therefore, they aren't really mortal anymore.
yes, I know pure mortal is a purely mechanical thing, but it can bleed into the IC world if you want it. For example, I have a character in my group who's catch is free will, so any actions committed with a deliberate intent by a mortal (or other creature not bound by their nature... pretty much just mortals and PCs). Their toughness abilities are just a blessing from Freya to help protect him from the things outside of Midguard.
If it's just an aspect, then it's fine. it's not changing who THEY are, just what they can do. the moment it starts changing who they are... then they loose that two point bump.
If the knight of the winter court ever gets excommunicated, stripped of his status and denied his powers, I'd say that he'd effectively go back to being a pure mortal.