I guess it's possible. I mention it because I've seen arguments over HP fanfiction that went something like this:
Ron never would've said "mom," he always said "mum."
Well, look at page xxx (screenshot).
Deer in headlights. What have they done to these books?
In all fairness, when I first started learning English, it was the British variant, so I might not be the best person to speak about how British these books were.