Thoughts about "heads up" between applicant & program:
So I really want to send my top choice(s) a polite, relevant, gracious email stating explicitly that my interest remains in the same area stated on my application despite the possibility of several other training possibilities available at their site...having learned of the varied options during the interview/OH.
What do others' think? Is this violating APPIC? I'm not giving them my rank order - just explicitly stating where I see myself in their 4-6 (let's just say...) available positions.
Or should I leave well-enough alone and chill?
Not a violation if you don't give them specific ranking information (i.e., where you plan to rank them). If however, you want them to know that you think you "fit better" in Track A than in Track B, you're walking a fine line.
I'm not sure how contacting them will help you? If each of their tracks or whatever has a separate APPIC number, then they'll rank you as they like for each possible track. You rank their tracks in order of your preference, and theoretically the algorithm starts with your list.