My situation was a little different but I still managed to get a grade change so I thought I'd post it.
My month of family medicine was included in my medicine grade. My preceptor adored me, took me out to dinner, showed me her dollhouse collection, etc. But I got my grade back from her and it was a high pass. I was pissed, because it lowered my grade in medicine from H to HP.
First I just thought she was one of those people who reserved honors for the absolute best student she'd ever seen, and just got pissed at the absurdity of it all (medicine was my first rotation - I hadn't learned yet that third year grades have basically no correlation to your performance.) Regardless, I hemmed and hawed for a bit, talked to my course director who said, "Well, she gave you what she gave you. You can talk to her about it if you want. Maybe you should have done better on your shelf, hint hint." Which pissed me off more because it was true.
But I called her at home and we got around to talking about my grade and it turns out she thought high pass was the best you could get. So she called my course director and had him change the grade and I got my honors. 🙂
So it can be done. Like I said, though, this was sort of a different situation.